array.c

/**********************************************************************

  array.c -

  $Author$
  created at: Fri Aug  6 09:46:12 JST 1993

  Copyright (C) 1993-2007 Yukihiro Matsumoto
  Copyright (C) 2000  Network Applied Communication Laboratory, Inc.
  Copyright (C) 2000  Information-technology Promotion Agency, Japan

**********************************************************************/

#include "ruby/ruby.h"
#include "ruby/util.h"
#include "ruby/st.h"
#include "ruby/encoding.h"
#include "internal.h"

#ifndef ARRAY_DEBUG
# define NDEBUG
#endif
#include <assert.h>

#define numberof(array) (int)(sizeof(array) / sizeof((array)[0]))

VALUE rb_cArray;

static ID id_cmp;

#define ARY_DEFAULT_SIZE 16
#define ARY_MAX_SIZE (LONG_MAX / (int)sizeof(VALUE))

void
rb_mem_clear(register VALUE *mem, register long size)
{
    while (size--) {
	*mem++ = Qnil;
    }
}

static inline void
memfill(register VALUE *mem, register long size, register VALUE val)
{
    while (size--) {
	*mem++ = val;
    }
}

# define ARY_SHARED_P(ary) \
    (assert(!FL_TEST((ary), ELTS_SHARED) || !FL_TEST((ary), RARRAY_EMBED_FLAG)), \
     FL_TEST((ary),ELTS_SHARED)!=0)
# define ARY_EMBED_P(ary) \
    (assert(!FL_TEST((ary), ELTS_SHARED) || !FL_TEST((ary), RARRAY_EMBED_FLAG)), \
     FL_TEST((ary), RARRAY_EMBED_FLAG)!=0)

#define ARY_HEAP_PTR(a) (assert(!ARY_EMBED_P(a)), RARRAY(a)->as.heap.ptr)
#define ARY_HEAP_LEN(a) (assert(!ARY_EMBED_P(a)), RARRAY(a)->as.heap.len)
#define ARY_EMBED_PTR(a) (assert(ARY_EMBED_P(a)), RARRAY(a)->as.ary)
#define ARY_EMBED_LEN(a) \
    (assert(ARY_EMBED_P(a)), \
     (long)((RBASIC(a)->flags >> RARRAY_EMBED_LEN_SHIFT) & \
	 (RARRAY_EMBED_LEN_MASK >> RARRAY_EMBED_LEN_SHIFT)))

#define ARY_OWNS_HEAP_P(a) (!FL_TEST((a), ELTS_SHARED|RARRAY_EMBED_FLAG))
#define FL_SET_EMBED(a) do { \
    assert(!ARY_SHARED_P(a)); \
    assert(!OBJ_FROZEN(a)); \
    FL_SET((a), RARRAY_EMBED_FLAG); \
} while (0)
#define FL_UNSET_EMBED(ary) FL_UNSET((ary), RARRAY_EMBED_FLAG|RARRAY_EMBED_LEN_MASK)
#define FL_SET_SHARED(ary) do { \
    assert(!ARY_EMBED_P(ary)); \
    FL_SET((ary), ELTS_SHARED); \
} while (0)
#define FL_UNSET_SHARED(ary) FL_UNSET((ary), ELTS_SHARED)

#define ARY_SET_PTR(ary, p) do { \
    assert(!ARY_EMBED_P(ary)); \
    assert(!OBJ_FROZEN(ary)); \
    RARRAY(ary)->as.heap.ptr = (p); \
} while (0)
#define ARY_SET_EMBED_LEN(ary, n) do { \
    long tmp_n = (n); \
    assert(ARY_EMBED_P(ary)); \
    assert(!OBJ_FROZEN(ary)); \
    RBASIC(ary)->flags &= ~RARRAY_EMBED_LEN_MASK; \
    RBASIC(ary)->flags |= (tmp_n) << RARRAY_EMBED_LEN_SHIFT; \
} while (0)
#define ARY_SET_HEAP_LEN(ary, n) do { \
    assert(!ARY_EMBED_P(ary)); \
    RARRAY(ary)->as.heap.len = (n); \
} while (0)
#define ARY_SET_LEN(ary, n) do { \
    if (ARY_EMBED_P(ary)) { \
        ARY_SET_EMBED_LEN((ary), (n)); \
    } \
    else { \
        ARY_SET_HEAP_LEN((ary), (n)); \
    } \
    assert(RARRAY_LEN(ary) == (n)); \
} while (0)
#define ARY_INCREASE_PTR(ary, n) do  { \
    assert(!ARY_EMBED_P(ary)); \
    assert(!OBJ_FROZEN(ary)); \
    RARRAY(ary)->as.heap.ptr += (n); \
} while (0)
#define ARY_INCREASE_LEN(ary, n) do  { \
    assert(!OBJ_FROZEN(ary)); \
    if (ARY_EMBED_P(ary)) { \
        ARY_SET_EMBED_LEN((ary), RARRAY_LEN(ary)+(n)); \
    } \
    else { \
        RARRAY(ary)->as.heap.len += (n); \
    } \
} while (0)

#define ARY_CAPA(ary) (ARY_EMBED_P(ary) ? RARRAY_EMBED_LEN_MAX : \
		       ARY_SHARED_ROOT_P(ary) ? RARRAY_LEN(ary) : RARRAY(ary)->as.heap.aux.capa)
#define ARY_SET_CAPA(ary, n) do { \
    assert(!ARY_EMBED_P(ary)); \
    assert(!ARY_SHARED_P(ary)); \
    assert(!OBJ_FROZEN(ary)); \
    RARRAY(ary)->as.heap.aux.capa = (n); \
} while (0)

#define ARY_SHARED(ary) (assert(ARY_SHARED_P(ary)), RARRAY(ary)->as.heap.aux.shared)
#define ARY_SET_SHARED(ary, value) do { \
    assert(!ARY_EMBED_P(ary)); \
    assert(ARY_SHARED_P(ary)); \
    assert(ARY_SHARED_ROOT_P(value)); \
    RARRAY(ary)->as.heap.aux.shared = (value); \
} while (0)
#define RARRAY_SHARED_ROOT_FLAG FL_USER5
#define ARY_SHARED_ROOT_P(ary) (FL_TEST((ary), RARRAY_SHARED_ROOT_FLAG))
#define ARY_SHARED_NUM(ary) \
    (assert(ARY_SHARED_ROOT_P(ary)), RARRAY(ary)->as.heap.aux.capa)
#define ARY_SET_SHARED_NUM(ary, value) do { \
    assert(ARY_SHARED_ROOT_P(ary)); \
    RARRAY(ary)->as.heap.aux.capa = (value); \
} while (0)
#define FL_SET_SHARED_ROOT(ary) do { \
    assert(!ARY_EMBED_P(ary)); \
    FL_SET((ary), RARRAY_SHARED_ROOT_FLAG); \
} while (0)

static void
ary_resize_capa(VALUE ary, long capacity)
{
    assert(RARRAY_LEN(ary) <= capacity);
    assert(!OBJ_FROZEN(ary));
    assert(!ARY_SHARED_P(ary));
    if (capacity > RARRAY_EMBED_LEN_MAX) {
        if (ARY_EMBED_P(ary)) {
            long len = ARY_EMBED_LEN(ary);
            VALUE *ptr = ALLOC_N(VALUE, (capacity));
            MEMCPY(ptr, ARY_EMBED_PTR(ary), VALUE, len);
            FL_UNSET_EMBED(ary);
            ARY_SET_PTR(ary, ptr);
            ARY_SET_HEAP_LEN(ary, len);
        }
        else {
            REALLOC_N(RARRAY(ary)->as.heap.ptr, VALUE, (capacity));
        }
        ARY_SET_CAPA(ary, (capacity));
    }
    else {
        if (!ARY_EMBED_P(ary)) {
            long len = RARRAY_LEN(ary);
            VALUE *ptr = RARRAY_PTR(ary);
            if (len > capacity) len = capacity;
            MEMCPY(RARRAY(ary)->as.ary, ptr, VALUE, len);
            FL_SET_EMBED(ary);
            ARY_SET_LEN(ary, len);
            xfree(ptr);
        }
    }
}

static void
ary_double_capa(VALUE ary, long min)
{
    long new_capa = ARY_CAPA(ary) / 2;

    if (new_capa < ARY_DEFAULT_SIZE) {
	new_capa = ARY_DEFAULT_SIZE;
    }
    if (new_capa >= ARY_MAX_SIZE - min) {
	new_capa = (ARY_MAX_SIZE - min) / 2;
    }
    new_capa += min;
    ary_resize_capa(ary, new_capa);
}

static void
rb_ary_decrement_share(VALUE shared)
{
    if (shared) {
	long num = ARY_SHARED_NUM(shared) - 1;
	if (num == 0) {
	    rb_ary_free(shared);
	    rb_gc_force_recycle(shared);
	}
	else if (num > 0) {
	    ARY_SET_SHARED_NUM(shared, num);
	}
    }
}

static void
rb_ary_unshare(VALUE ary)
{
    VALUE shared = RARRAY(ary)->as.heap.aux.shared;
    rb_ary_decrement_share(shared);
    FL_UNSET_SHARED(ary);
}

static inline void
rb_ary_unshare_safe(VALUE ary)
{
    if (ARY_SHARED_P(ary) && !ARY_EMBED_P(ary)) {
	rb_ary_unshare(ary);
    }
}

static VALUE
rb_ary_increment_share(VALUE shared)
{
    long num = ARY_SHARED_NUM(shared);
    if (num >= 0) {
	ARY_SET_SHARED_NUM(shared, num + 1);
    }
    return shared;
}

static void
rb_ary_set_shared(VALUE ary, VALUE shared)
{
    rb_ary_increment_share(shared);
    FL_SET_SHARED(ary);
    ARY_SET_SHARED(ary, shared);
}

static inline void
rb_ary_modify_check(VALUE ary)
{
    rb_check_frozen(ary);
    if (!OBJ_UNTRUSTED(ary) && rb_safe_level() >= 4)
	rb_raise(rb_eSecurityError, "Insecure: can't modify array");
}

void
rb_ary_modify(VALUE ary)
{
    rb_ary_modify_check(ary);
    if (ARY_SHARED_P(ary)) {
        long len = RARRAY_LEN(ary);
        if (len <= RARRAY_EMBED_LEN_MAX) {
            VALUE *ptr = ARY_HEAP_PTR(ary);
            VALUE shared = ARY_SHARED(ary);
            FL_UNSET_SHARED(ary);
            FL_SET_EMBED(ary);
            MEMCPY(ARY_EMBED_PTR(ary), ptr, VALUE, len);
            rb_ary_decrement_share(shared);
            ARY_SET_EMBED_LEN(ary, len);
        }
        else {
            VALUE *ptr = ALLOC_N(VALUE, len);
            MEMCPY(ptr, RARRAY_PTR(ary), VALUE, len);
            rb_ary_unshare(ary);
            ARY_SET_CAPA(ary, len);
            ARY_SET_PTR(ary, ptr);
        }
    }
}

/*
 *  call-seq:
 *      ary.freeze -> ary
 *
 *  Calls Object#freeze on +ary+ to prevent any further
 *  modification. A RuntimeError will be raised if a modification
 *  attempt is made.
 *
 */

VALUE
rb_ary_freeze(VALUE ary)
{
    return rb_obj_freeze(ary);
}

/*
 *  call-seq:
 *     ary.frozen?  -> true or false
 *
 *  Return +true+ if this array is frozen (or temporarily frozen
 *  while being sorted). See also Object#frozen?
 */

static VALUE
rb_ary_frozen_p(VALUE ary)
{
    if (OBJ_FROZEN(ary)) return Qtrue;
    return Qfalse;
}

static VALUE
ary_alloc(VALUE klass)
{
    NEWOBJ_OF(ary, struct RArray, klass, T_ARRAY);
    FL_SET_EMBED((VALUE)ary);
    ARY_SET_EMBED_LEN((VALUE)ary, 0);

    return (VALUE)ary;
}

static VALUE
ary_new(VALUE klass, long capa)
{
    VALUE ary;

    if (capa < 0) {
	rb_raise(rb_eArgError, "negative array size (or size too big)");
    }
    if (capa > ARY_MAX_SIZE) {
	rb_raise(rb_eArgError, "array size too big");
    }
    ary = ary_alloc(klass);
    if (capa > RARRAY_EMBED_LEN_MAX) {
        FL_UNSET_EMBED(ary);
        ARY_SET_PTR(ary, ALLOC_N(VALUE, capa));
        ARY_SET_CAPA(ary, capa);
        ARY_SET_HEAP_LEN(ary, 0);
    }

    return ary;
}

VALUE
rb_ary_new2(long capa)
{
    return ary_new(rb_cArray, capa);
}


VALUE
rb_ary_new(void)
{
    return rb_ary_new2(RARRAY_EMBED_LEN_MAX);
}

#include <stdarg.h>

VALUE
rb_ary_new3(long n, ...)
{
    va_list ar;
    VALUE ary;
    long i;

    ary = rb_ary_new2(n);

    va_start(ar, n);
    for (i=0; i<n; i++) {
	RARRAY_PTR(ary)[i] = va_arg(ar, VALUE);
    }
    va_end(ar);

    ARY_SET_LEN(ary, n);
    return ary;
}

VALUE
rb_ary_new4(long n, const VALUE *elts)
{
    VALUE ary;

    ary = rb_ary_new2(n);
    if (n > 0 && elts) {
	MEMCPY(RARRAY_PTR(ary), elts, VALUE, n);
	ARY_SET_LEN(ary, n);
    }

    return ary;
}

VALUE
rb_ary_tmp_new(long capa)
{
    return ary_new(0, capa);
}

void
rb_ary_free(VALUE ary)
{
    if (ARY_OWNS_HEAP_P(ary)) {
	xfree(ARY_HEAP_PTR(ary));
    }
}

RUBY_FUNC_EXPORTED size_t
rb_ary_memsize(VALUE ary)
{
    if (ARY_OWNS_HEAP_P(ary)) {
	return RARRAY(ary)->as.heap.aux.capa * sizeof(VALUE);
    }
    else {
	return 0;
    }
}

static inline void
ary_discard(VALUE ary)
{
    rb_ary_free(ary);
    RBASIC(ary)->flags |= RARRAY_EMBED_FLAG;
    RBASIC(ary)->flags &= ~RARRAY_EMBED_LEN_MASK;
}

static VALUE
ary_make_shared(VALUE ary)
{
    assert(!ARY_EMBED_P(ary));
    if (ARY_SHARED_P(ary)) {
	return ARY_SHARED(ary);
    }
    else if (ARY_SHARED_ROOT_P(ary)) {
	return ary;
    }
    else if (OBJ_FROZEN(ary)) {
	ary_resize_capa(ary, ARY_HEAP_LEN(ary));
	FL_SET_SHARED_ROOT(ary);
	ARY_SET_SHARED_NUM(ary, 1);
	return ary;
    }
    else {
	NEWOBJ_OF(shared, struct RArray, 0, T_ARRAY);
        FL_UNSET_EMBED(shared);

        ARY_SET_LEN((VALUE)shared, RARRAY_LEN(ary));
        ARY_SET_PTR((VALUE)shared, RARRAY_PTR(ary));
	FL_SET_SHARED_ROOT(shared);
	ARY_SET_SHARED_NUM((VALUE)shared, 1);
	FL_SET_SHARED(ary);
	ARY_SET_SHARED(ary, (VALUE)shared);
	OBJ_FREEZE(shared);
	return (VALUE)shared;
    }
}


static VALUE
ary_make_substitution(VALUE ary)
{
    if (RARRAY_LEN(ary) <= RARRAY_EMBED_LEN_MAX) {
        VALUE subst = rb_ary_new2(RARRAY_LEN(ary));
        MEMCPY(ARY_EMBED_PTR(subst), RARRAY_PTR(ary), VALUE, RARRAY_LEN(ary));
        ARY_SET_EMBED_LEN(subst, RARRAY_LEN(ary));
        return subst;
    }
    else {
        return rb_ary_increment_share(ary_make_shared(ary));
    }
}

VALUE
rb_assoc_new(VALUE car, VALUE cdr)
{
    return rb_ary_new3(2, car, cdr);
}

static VALUE
to_ary(VALUE ary)
{
    return rb_convert_type(ary, T_ARRAY, "Array", "to_ary");
}

VALUE
rb_check_array_type(VALUE ary)
{
    return rb_check_convert_type(ary, T_ARRAY, "Array", "to_ary");
}

/*
 *  call-seq:
 *     Array.try_convert(obj) -> array or nil
 *
 *  Tries to convert +obj+ into an array, using +to_ary+ method.  Returns the
 *  converted array or +nil+ if +obj+ cannot be converted for any reason.
 *  This method can be used to check if an argument is an array.
 *
 *     Array.try_convert([1])   #=> [1]
 *     Array.try_convert("1")   #=> nil
 *
 *     if tmp = Array.try_convert(arg)
 *       # the argument is an array
 *     elsif tmp = String.try_convert(arg)
 *       # the argument is a string
 *     end
 *
 */

static VALUE
rb_ary_s_try_convert(VALUE dummy, VALUE ary)
{
    return rb_check_array_type(ary);
}

/*
 *  call-seq:
 *     Array.new(size=0, obj=nil)
 *     Array.new(array)
 *     Array.new(size) {|index| block }
 *
 *  Returns a new array.
 *
 *  In the first form, if no arguments are sent, the new array will be empty.
 *  When a +size+ and an optional +obj+ are sent, an array is created with
 *  +size+ copies of +obj+.  Take notice that all elements will reference the
 *  same object +obj+.
 *
 *  The second form creates a copy of the array passed as a parameter (the
 *  array is generated by calling to_ary on the parameter).
 *
 *    first_array = ["Matz", "Guido"]
 *
 *    second_array = Array.new(first_array) #=> ["Matz", "Guido"]
 *
 *    first_array.equal? second_array       #=> false
 *
 *  In the last form, an array of the given size is created.  Each element in
 *  this array is created by passing the element's index to the given block
 *  and storing the return value.
 *
 *    Array.new(3){ |index| index ** 2 }
 *    # => [0, 1, 4]
 *
 *  == Common gotchas
 *
 *  When sending the second parameter, the same object will be used as the
 *  value for all the array elements:
 *
 *     a = Array.new(2, Hash.new)
 *     # => [{}, {}]
 *
 *     a[0]['cat'] = 'feline'
 *     a # => [{"cat"=>"feline"}, {"cat"=>"feline"}]
 *
 *     a[1]['cat'] = 'Felix'
 *     a # => [{"cat"=>"Felix"}, {"cat"=>"Felix"}]
 *
 *  Since all the Array elements store the same hash, changes to one of them
 *  will affect them all.
 *
 *  If multiple copies are what you want, you should use the block
 *  version which uses the result of that block each time an element
 *  of the array needs to be initialized:
 *
 *     a = Array.new(2) { Hash.new }
 *     a[0]['cat'] = 'feline'
 *     a # => [{"cat"=>"feline"}, {}]
 *
 */

static VALUE
rb_ary_initialize(int argc, VALUE *argv, VALUE ary)
{
    long len;
    VALUE size, val;

    rb_ary_modify(ary);
    if (argc == 0) {
	if (ARY_OWNS_HEAP_P(ary) && RARRAY_PTR(ary)) {
	    xfree(RARRAY_PTR(ary));
	}
        rb_ary_unshare_safe(ary);
        FL_SET_EMBED(ary);
	ARY_SET_EMBED_LEN(ary, 0);
	if (rb_block_given_p()) {
	    rb_warning("given block not used");
	}
	return ary;
    }
    rb_scan_args(argc, argv, "02", &size, &val);
    if (argc == 1 && !FIXNUM_P(size)) {
	val = rb_check_array_type(size);
	if (!NIL_P(val)) {
	    rb_ary_replace(ary, val);
	    return ary;
	}
    }

    len = NUM2LONG(size);
    if (len < 0) {
	rb_raise(rb_eArgError, "negative array size");
    }
    if (len > ARY_MAX_SIZE) {
	rb_raise(rb_eArgError, "array size too big");
    }
    rb_ary_modify(ary);
    ary_resize_capa(ary, len);
    if (rb_block_given_p()) {
	long i;

	if (argc == 2) {
	    rb_warn("block supersedes default value argument");
	}
	for (i=0; i<len; i++) {
	    rb_ary_store(ary, i, rb_yield(LONG2NUM(i)));
	    ARY_SET_LEN(ary, i + 1);
	}
    }
    else {
	memfill(RARRAY_PTR(ary), len, val);
	ARY_SET_LEN(ary, len);
    }
    return ary;
}

/*
 * Returns a new array populated with the given objects.
 *
 *   Array.[]( 1, 'a', /^A/ ) # => [1, "a", /^A/]
 *   Array[ 1, 'a', /^A/ ]    # => [1, "a", /^A/]
 *   [ 1, 'a', /^A/ ]         # => [1, "a", /^A/]
 */

static VALUE
rb_ary_s_create(int argc, VALUE *argv, VALUE klass)
{
    VALUE ary = ary_new(klass, argc);
    if (argc > 0 && argv) {
        MEMCPY(RARRAY_PTR(ary), argv, VALUE, argc);
        ARY_SET_LEN(ary, argc);
    }

    return ary;
}

void
rb_ary_store(VALUE ary, long idx, VALUE val)
{
    if (idx < 0) {
	idx += RARRAY_LEN(ary);
	if (idx < 0) {
	    rb_raise(rb_eIndexError, "index %ld too small for array; minimum: %ld",
		     idx - RARRAY_LEN(ary), -RARRAY_LEN(ary));
	}
    }
    else if (idx >= ARY_MAX_SIZE) {
	rb_raise(rb_eIndexError, "index %ld too big", idx);
    }

    rb_ary_modify(ary);
    if (idx >= ARY_CAPA(ary)) {
	ary_double_capa(ary, idx);
    }
    if (idx > RARRAY_LEN(ary)) {
	rb_mem_clear(RARRAY_PTR(ary) + RARRAY_LEN(ary),
		     idx-RARRAY_LEN(ary) + 1);
    }

    if (idx >= RARRAY_LEN(ary)) {
	ARY_SET_LEN(ary, idx + 1);
    }
    RARRAY_PTR(ary)[idx] = val;
}

static VALUE
ary_make_partial(VALUE ary, VALUE klass, long offset, long len)
{
    assert(offset >= 0);
    assert(len >= 0);
    assert(offset+len <= RARRAY_LEN(ary));

    if (len <= RARRAY_EMBED_LEN_MAX) {
        VALUE result = ary_alloc(klass);
        MEMCPY(ARY_EMBED_PTR(result), RARRAY_PTR(ary) + offset, VALUE, len);
        ARY_SET_EMBED_LEN(result, len);
        return result;
    }
    else {
        VALUE shared, result = ary_alloc(klass);
        FL_UNSET_EMBED(result);

        shared = ary_make_shared(ary);
        ARY_SET_PTR(result, RARRAY_PTR(ary));
        ARY_SET_LEN(result, RARRAY_LEN(ary));
        rb_ary_set_shared(result, shared);

        ARY_INCREASE_PTR(result, offset);
        ARY_SET_LEN(result, len);
        return result;
    }
}

static VALUE
ary_make_shared_copy(VALUE ary)
{
    return ary_make_partial(ary, rb_obj_class(ary), 0, RARRAY_LEN(ary));
}

enum ary_take_pos_flags
{
    ARY_TAKE_FIRST = 0,
    ARY_TAKE_LAST = 1
};

static VALUE
ary_take_first_or_last(int argc, VALUE *argv, VALUE ary, enum ary_take_pos_flags last)
{
    VALUE nv;
    long n;
    long offset = 0;

    rb_scan_args(argc, argv, "1", &nv);
    n = NUM2LONG(nv);
    if (n > RARRAY_LEN(ary)) {
	n = RARRAY_LEN(ary);
    }
    else if (n < 0) {
	rb_raise(rb_eArgError, "negative array size");
    }
    if (last) {
	offset = RARRAY_LEN(ary) - n;
    }
    return ary_make_partial(ary, rb_cArray, offset, n);
}

static VALUE rb_ary_push_1(VALUE ary, VALUE item);

/*
 *  call-seq:
 *     ary << obj            -> ary
 *
 *  Append---Pushes the given object on to the end of this array. This
 *  expression returns the array itself, so several appends
 *  may be chained together.
 *
 *     [ 1, 2 ] << "c" << "d" << [ 3, 4 ]
 *             #=>  [ 1, 2, "c", "d", [ 3, 4 ] ]
 *
 */

VALUE
rb_ary_push(VALUE ary, VALUE item)
{
    rb_ary_modify(ary);
    return rb_ary_push_1(ary, item);
}

static VALUE
rb_ary_push_1(VALUE ary, VALUE item)
{
    long idx = RARRAY_LEN(ary);

    if (idx >= ARY_CAPA(ary)) {
	ary_double_capa(ary, idx);
    }
    RARRAY_PTR(ary)[idx] = item;
    ARY_SET_LEN(ary, idx + 1);
    return ary;
}

VALUE
rb_ary_cat(VALUE ary, const VALUE *ptr, long len)
{
    long oldlen;

    rb_ary_modify(ary);
    oldlen = RARRAY_LEN(ary);
    ary_resize_capa(ary, oldlen + len);
    MEMCPY(RARRAY_PTR(ary) + oldlen, ptr, VALUE, len);
    ARY_SET_LEN(ary, oldlen + len);
    return ary;
}

/*
 *  call-seq:
 *     ary.push(obj, ... )   -> ary
 *
 *  Append --- Pushes the given object(s) on to the end of this array. This
 *  expression returns the array itself, so several appends
 *  may be chained together. See also Array#pop for the opposite
 *  effect.
 *
 *     a = [ "a", "b", "c" ]
 *     a.push("d", "e", "f")
 *             #=> ["a", "b", "c", "d", "e", "f"]
 *     [1, 2, 3,].push(4).push(5)
 *             #=> [1, 2, 3, 4, 5]
 */

static VALUE
rb_ary_push_m(int argc, VALUE *argv, VALUE ary)
{
    return rb_ary_cat(ary, argv, argc);
}

VALUE
rb_ary_pop(VALUE ary)
{
    long n;
    rb_ary_modify_check(ary);
    if (RARRAY_LEN(ary) == 0) return Qnil;
    if (ARY_OWNS_HEAP_P(ary) &&
	RARRAY_LEN(ary) * 3 < ARY_CAPA(ary) &&
	ARY_CAPA(ary) > ARY_DEFAULT_SIZE)
    {
	ary_resize_capa(ary, RARRAY_LEN(ary) * 2);
    }
    n = RARRAY_LEN(ary)-1;
    ARY_SET_LEN(ary, n);
    return RARRAY_PTR(ary)[n];
}

/*
 *  call-seq:
 *     ary.pop    -> obj or nil
 *     ary.pop(n) -> new_ary
 *
 *  Removes the last element from +self+ and returns it, or
 *  +nil+ if the array is empty.
 *
 *  If a number +n+ is given, returns an array of the last +n+ elements
 *  (or less) just like <code>array.slice!(-n, n)</code> does. See also
 *  Array#push for the opposite effect.
 *
 *     a = [ "a", "b", "c", "d" ]
 *     a.pop     #=> "d"
 *     a.pop(2)  #=> ["b", "c"]
 *     a         #=> ["a"]
 */

static VALUE
rb_ary_pop_m(int argc, VALUE *argv, VALUE ary)
{
    VALUE result;

    if (argc == 0) {
	return rb_ary_pop(ary);
    }

    rb_ary_modify_check(ary);
    result = ary_take_first_or_last(argc, argv, ary, ARY_TAKE_LAST);
    ARY_INCREASE_LEN(ary, -RARRAY_LEN(result));
    return result;
}

VALUE
rb_ary_shift(VALUE ary)
{
    VALUE top;

    rb_ary_modify_check(ary);
    if (RARRAY_LEN(ary) == 0) return Qnil;
    top = RARRAY_PTR(ary)[0];
    if (!ARY_SHARED_P(ary)) {
	if (RARRAY_LEN(ary) < ARY_DEFAULT_SIZE) {
	    MEMMOVE(RARRAY_PTR(ary), RARRAY_PTR(ary)+1, VALUE, RARRAY_LEN(ary)-1);
            ARY_INCREASE_LEN(ary, -1);
	    return top;
	}
        assert(!ARY_EMBED_P(ary)); /* ARY_EMBED_LEN_MAX < ARY_DEFAULT_SIZE */

	RARRAY_PTR(ary)[0] = Qnil;
	ary_make_shared(ary);
    }
    else if (ARY_SHARED_NUM(ARY_SHARED(ary)) == 1) {
	RARRAY_PTR(ary)[0] = Qnil;
    }
    ARY_INCREASE_PTR(ary, 1);		/* shift ptr */
    ARY_INCREASE_LEN(ary, -1);

    return top;
}

/*
 *  call-seq:
 *     ary.shift    -> obj or nil
 *     ary.shift(n) -> new_ary
 *
 *  Removes the first element of +self+ and returns it (shifting all
 *  other elements down by one). Returns +nil+ if the array
 *  is empty.
 *
 *  If a number +n+ is given, returns an array of the first +n+ elements
 *  (or less) just like <code>array.slice!(0, n)</code> does. With +ary+
 *  containing only the remainder elements, not including what was shifted to
 *  +new_ary+. See also Array#unshift for the opposite effect.
 *
 *     args = [ "-m", "-q", "filename" ]
 *     args.shift     #=> "-m"
 *     args           #=> ["-q", "filename"]
 *
 *     args = [ "-m", "-q", "filename" ]
 *     args.shift(2)  #=> ["-m", "-q"]
 *     args           #=> ["filename"]
 */

static VALUE
rb_ary_shift_m(int argc, VALUE *argv, VALUE ary)
{
    VALUE result;
    long n;

    if (argc == 0) {
	return rb_ary_shift(ary);
    }

    rb_ary_modify_check(ary);
    result = ary_take_first_or_last(argc, argv, ary, ARY_TAKE_FIRST);
    n = RARRAY_LEN(result);
    if (ARY_SHARED_P(ary)) {
	if (ARY_SHARED_NUM(ARY_SHARED(ary)) == 1) {
	    rb_mem_clear(RARRAY_PTR(ary), n);
	}
        ARY_INCREASE_PTR(ary, n);
    }
    else {
	MEMMOVE(RARRAY_PTR(ary), RARRAY_PTR(ary)+n, VALUE, RARRAY_LEN(ary)-n);
    }
    ARY_INCREASE_LEN(ary, -n);

    return result;
}

/*
 *  call-seq:
 *     ary.unshift(obj, ...)  -> ary
 *
 *  Prepends objects to the front of +self+, moving other elements upwards.
 *  See also Array#shift for the opposite effect.
 *
 *     a = [ "b", "c", "d" ]
 *     a.unshift("a")   #=> ["a", "b", "c", "d"]
 *     a.unshift(1, 2)  #=> [ 1, 2, "a", "b", "c", "d"]
 */

static VALUE
rb_ary_unshift_m(int argc, VALUE *argv, VALUE ary)
{
    long len;

    rb_ary_modify(ary);
    if (argc == 0) return ary;
    if (ARY_CAPA(ary) <= (len = RARRAY_LEN(ary)) + argc) {
	ary_double_capa(ary, len + argc);
    }

    /* sliding items */
    MEMMOVE(RARRAY_PTR(ary) + argc, RARRAY_PTR(ary), VALUE, len);
    MEMCPY(RARRAY_PTR(ary), argv, VALUE, argc);
    ARY_INCREASE_LEN(ary, argc);

    return ary;
}

VALUE
rb_ary_unshift(VALUE ary, VALUE item)
{
    return rb_ary_unshift_m(1,&item,ary);
}

/* faster version - use this if you don't need to treat negative offset */
static inline VALUE
rb_ary_elt(VALUE ary, long offset)
{
    if (RARRAY_LEN(ary) == 0) return Qnil;
    if (offset < 0 || RARRAY_LEN(ary) <= offset) {
	return Qnil;
    }
    return RARRAY_PTR(ary)[offset];
}

VALUE
rb_ary_entry(VALUE ary, long offset)
{
    if (offset < 0) {
	offset += RARRAY_LEN(ary);
    }
    return rb_ary_elt(ary, offset);
}

VALUE
rb_ary_subseq(VALUE ary, long beg, long len)
{
    VALUE klass;

    if (beg > RARRAY_LEN(ary)) return Qnil;
    if (beg < 0 || len < 0) return Qnil;

    if (RARRAY_LEN(ary) < len || RARRAY_LEN(ary) < beg + len) {
	len = RARRAY_LEN(ary) - beg;
    }
    klass = rb_obj_class(ary);
    if (len == 0) return ary_new(klass, 0);

    return ary_make_partial(ary, klass, beg, len);
}

/*
 *  call-seq:
 *     ary[index]                -> obj     or nil
 *     ary[start, length]        -> new_ary or nil
 *     ary[range]                -> new_ary or nil
 *     ary.slice(index)          -> obj     or nil
 *     ary.slice(start, length)  -> new_ary or nil
 *     ary.slice(range)          -> new_ary or nil
 *
 *  Element Reference --- Returns the element at +index+, or returns a
 *  subarray starting at the +start+ index and continuing for +length+
 *  elements, or returns a subarray specified by +range+ of indices.
 *
 *  Negative indices count backward from the end of the array (-1 is the last
 *  element).  For +start+ and +range+ cases the starting index is just before
 *  an element.  Additionally, an empty array is returned when the starting
 *  index for an element range is at the end of the array.
 *
 *  Returns +nil+ if the index (or starting index) are out of range.
 *
 *     a = [ "a", "b", "c", "d", "e" ]
 *     a[2] +  a[0] + a[1]    #=> "cab"
 *     a[6]                   #=> nil
 *     a[1, 2]                #=> [ "b", "c" ]
 *     a[1..3]                #=> [ "b", "c", "d" ]
 *     a[4..7]                #=> [ "e" ]
 *     a[6..10]               #=> nil
 *     a[-3, 3]               #=> [ "c", "d", "e" ]
 *     # special cases
 *     a[5]                   #=> nil
 *     a[6, 1]                #=> nil
 *     a[5, 1]                #=> []
 *     a[5..10]               #=> []
 *
 */

VALUE
rb_ary_aref(int argc, VALUE *argv, VALUE ary)
{
    VALUE arg;
    long beg, len;

    if (argc == 2) {
	beg = NUM2LONG(argv[0]);
	len = NUM2LONG(argv[1]);
	if (beg < 0) {
	    beg += RARRAY_LEN(ary);
	}
	return rb_ary_subseq(ary, beg, len);
    }
    if (argc != 1) {
	rb_scan_args(argc, argv, "11", 0, 0);
    }
    arg = argv[0];
    /* special case - speeding up */
    if (FIXNUM_P(arg)) {
	return rb_ary_entry(ary, FIX2LONG(arg));
    }
    /* check if idx is Range */
    switch (rb_range_beg_len(arg, &beg, &len, RARRAY_LEN(ary), 0)) {
      case Qfalse:
	break;
      case Qnil:
	return Qnil;
      default:
	return rb_ary_subseq(ary, beg, len);
    }
    return rb_ary_entry(ary, NUM2LONG(arg));
}

/*
 *  call-seq:
 *     ary.at(index)   ->   obj  or nil
 *
 *  Returns the element at +index+. A negative index counts from the end of
 *  +self+. Returns +nil+ if the index is out of range. See also
 *  Array#[].
 *
 *     a = [ "a", "b", "c", "d", "e" ]
 *     a.at(0)     #=> "a"
 *     a.at(-1)    #=> "e"
 */

static VALUE
rb_ary_at(VALUE ary, VALUE pos)
{
    return rb_ary_entry(ary, NUM2LONG(pos));
}

/*
 *  call-seq:
 *     ary.first     ->   obj or nil
 *     ary.first(n)  ->   new_ary
 *
 *  Returns the first element, or the first +n+ elements, of the array.
 *  If the array is empty, the first form returns +nil+, and the
 *  second form returns an empty array. See also Array#last for
 *  the opposite effect.
 *
 *     a = [ "q", "r", "s", "t" ]
 *     a.first     #=> "q"
 *     a.first(2)  #=> ["q", "r"]
 */

static VALUE
rb_ary_first(int argc, VALUE *argv, VALUE ary)
{
    if (argc == 0) {
	if (RARRAY_LEN(ary) == 0) return Qnil;
	return RARRAY_PTR(ary)[0];
    }
    else {
	return ary_take_first_or_last(argc, argv, ary, ARY_TAKE_FIRST);
    }
}

/*
 *  call-seq:
 *     ary.last     ->  obj or nil
 *     ary.last(n)  ->  new_ary
 *
 *  Returns the last element(s) of +self+. If the array is empty,
 *  the first form returns +nil+.
 *
 *  See also Array#first for the opposite effect.
 *
 *     a = [ "w", "x", "y", "z" ]
 *     a.last     #=> "z"
 *     a.last(2)  #=> ["y", "z"]
 */

VALUE
rb_ary_last(int argc, VALUE *argv, VALUE ary)
{
    if (argc == 0) {
	if (RARRAY_LEN(ary) == 0) return Qnil;
	return RARRAY_PTR(ary)[RARRAY_LEN(ary)-1];
    }
    else {
	return ary_take_first_or_last(argc, argv, ary, ARY_TAKE_LAST);
    }
}

/*
 *  call-seq:
 *     ary.fetch(index)                    -> obj
 *     ary.fetch(index, default)           -> obj
 *     ary.fetch(index) { |index| block }  -> obj
 *
 *  Tries to return the element at position +index+, but throws an IndexError
 *  exception if the referenced +index+ lies outside of the array bounds.  This
 *  error can be prevented by supplying a second argument, which will act as a
 *  +default+ value.
 *
 *  Alternatively, if a block is given it will only be executed when an
 *  invalid +index+ is referenced.  Negative values of +index+ count from the
 *  end of the array.
 *
 *     a = [ 11, 22, 33, 44 ]
 *     a.fetch(1)               #=> 22
 *     a.fetch(-1)              #=> 44
 *     a.fetch(4, 'cat')        #=> "cat"
 *     a.fetch(100) { |i| puts "#{i} is out of bounds" }
 *                              #=> "100 is out of bounds"
 */

static VALUE
rb_ary_fetch(int argc, VALUE *argv, VALUE ary)
{
    VALUE pos, ifnone;
    long block_given;
    long idx;

    rb_scan_args(argc, argv, "11", &pos, &ifnone);
    block_given = rb_block_given_p();
    if (block_given && argc == 2) {
	rb_warn("block supersedes default value argument");
    }
    idx = NUM2LONG(pos);

    if (idx < 0) {
	idx +=  RARRAY_LEN(ary);
    }
    if (idx < 0 || RARRAY_LEN(ary) <= idx) {
	if (block_given) return rb_yield(pos);
	if (argc == 1) {
	    rb_raise(rb_eIndexError, "index %ld outside of array bounds: %ld...%ld",
			idx - (idx < 0 ? RARRAY_LEN(ary) : 0), -RARRAY_LEN(ary), RARRAY_LEN(ary));
	}
	return ifnone;
    }
    return RARRAY_PTR(ary)[idx];
}

/*
 *  call-seq:
 *     ary.index(obj)             ->  int or nil
 *     ary.index { |item| block } ->  int or nil
 *     ary.index                  ->  Enumerator
 *
 *  Returns the _index_ of the first object in +ary+ such that the object is
 *  <code>==</code> to +obj+.
 *
 *  If a block is given instead of an argument, returns the _index_ of first
 *  the object for which the block returns +true+.  Returns +nil+ if no match
 *  is found.
 *
 *  See also Array#rindex.
 *
 *  An Enumerator is returned if neither a block nor argument is given.
 *
 *     a = [ "a", "b", "c" ]
 *     a.index("b")              #=> 1
 *     a.index("z")              #=> nil
 *     a.index { |x| x == "b" }  #=> 1
 *
 *  This is an alias of Array#find_index.
 */

static VALUE
rb_ary_index(int argc, VALUE *argv, VALUE ary)
{
    VALUE val;
    long i;

    if (argc == 0) {
	RETURN_ENUMERATOR(ary, 0, 0);
	for (i=0; i<RARRAY_LEN(ary); i++) {
	    if (RTEST(rb_yield(RARRAY_PTR(ary)[i]))) {
		return LONG2NUM(i);
	    }
	}
	return Qnil;
    }
    rb_scan_args(argc, argv, "1", &val);
    if (rb_block_given_p())
	rb_warn("given block not used");
    for (i=0; i<RARRAY_LEN(ary); i++) {
	if (rb_equal(RARRAY_PTR(ary)[i], val))
	    return LONG2NUM(i);
    }
    return Qnil;
}

/*
 *  call-seq:
 *     ary.rindex(obj)             ->  int or nil
 *     ary.rindex { |item| block } ->  int or nil
 *     ary.rindex                  ->  Enumerator
 *
 *  Returns the _index_ of the last object in +self+ <code>==</code> to +obj+.
 *
 *  If a block is given instead of an argument, returns _index_ of first object
 *  for which block returns +true+, starting from the last object.
 *
 *  Returns +nil+ if no match is found.
 *
 *  See also Array#index.
 *
 *  If neither block nor argument is given, an Enumerator is returned instead.
 *
 *     a = [ "a", "b", "b", "b", "c" ]
 *     a.rindex("b")             #=> 3
 *     a.rindex("z")             #=> nil
 *     a.rindex { |x| x == "b" } #=> 3
 */

static VALUE
rb_ary_rindex(int argc, VALUE *argv, VALUE ary)
{
    VALUE val;
    long i = RARRAY_LEN(ary);

    if (argc == 0) {
	RETURN_ENUMERATOR(ary, 0, 0);
	while (i--) {
	    if (RTEST(rb_yield(RARRAY_PTR(ary)[i])))
		return LONG2NUM(i);
	    if (i > RARRAY_LEN(ary)) {
		i = RARRAY_LEN(ary);
	    }
	}
	return Qnil;
    }
    rb_scan_args(argc, argv, "1", &val);
    if (rb_block_given_p())
	rb_warn("given block not used");
    while (i--) {
	if (rb_equal(RARRAY_PTR(ary)[i], val))
	    return LONG2NUM(i);
	if (i > RARRAY_LEN(ary)) {
	    i = RARRAY_LEN(ary);
	}
    }
    return Qnil;
}

VALUE
rb_ary_to_ary(VALUE obj)
{
    VALUE tmp = rb_check_array_type(obj);

    if (!NIL_P(tmp)) return tmp;
    return rb_ary_new3(1, obj);
}

static void
rb_ary_splice(VALUE ary, long beg, long len, VALUE rpl)
{
    long rlen;

    if (len < 0) rb_raise(rb_eIndexError, "negative length (%ld)", len);
    if (beg < 0) {
	beg += RARRAY_LEN(ary);
	if (beg < 0) {
	    rb_raise(rb_eIndexError, "index %ld too small for array; minimum: %ld",
		     beg - RARRAY_LEN(ary), -RARRAY_LEN(ary));
	}
    }
    if (RARRAY_LEN(ary) < len || RARRAY_LEN(ary) < beg + len) {
	len = RARRAY_LEN(ary) - beg;
    }

    if (rpl == Qundef) {
	rlen = 0;
    }
    else {
	rpl = rb_ary_to_ary(rpl);
	rlen = RARRAY_LEN(rpl);
    }
    rb_ary_modify(ary);
    if (beg >= RARRAY_LEN(ary)) {
	if (beg > ARY_MAX_SIZE - rlen) {
	    rb_raise(rb_eIndexError, "index %ld too big", beg);
	}
	len = beg + rlen;
	if (len >= ARY_CAPA(ary)) {
	    ary_double_capa(ary, len);
	}
	rb_mem_clear(RARRAY_PTR(ary) + RARRAY_LEN(ary), beg - RARRAY_LEN(ary));
	if (rlen > 0) {
	    MEMCPY(RARRAY_PTR(ary) + beg, RARRAY_PTR(rpl), VALUE, rlen);
	}
	ARY_SET_LEN(ary, len);
    }
    else {
	long alen;

	alen = RARRAY_LEN(ary) + rlen - len;
	if (alen >= ARY_CAPA(ary)) {
	    ary_double_capa(ary, alen);
	}

	if (len != rlen) {
	    MEMMOVE(RARRAY_PTR(ary) + beg + rlen, RARRAY_PTR(ary) + beg + len,
		    VALUE, RARRAY_LEN(ary) - (beg + len));
	    ARY_SET_LEN(ary, alen);
	}
	if (rlen > 0) {
	    MEMMOVE(RARRAY_PTR(ary) + beg, RARRAY_PTR(rpl), VALUE, rlen);
	}
    }
}

void
rb_ary_set_len(VALUE ary, long len)
{
    long capa;

    rb_ary_modify_check(ary);
    if (ARY_SHARED_P(ary)) {
	rb_raise(rb_eRuntimeError, "can't set length of shared ");
    }
    if (len > (capa = (long)ARY_CAPA(ary))) {
	rb_bug("probable buffer overflow: %ld for %ld", len, capa);
    }
    ARY_SET_LEN(ary, len);
}

/*!
 * expands or shrinks \a ary to \a len elements.
 * expanded region will be filled with Qnil.
 * \param ary  an array
 * \param len  new size
 * \return     \a ary
 * \post       the size of \a ary is \a len.
 */
VALUE
rb_ary_resize(VALUE ary, long len)
{
    long olen;

    rb_ary_modify(ary);
    olen = RARRAY_LEN(ary);
    if (len == olen) return ary;
    if (len > ARY_MAX_SIZE) {
	rb_raise(rb_eIndexError, "index %ld too big", len);
    }
    if (len > olen) {
	if (len >= ARY_CAPA(ary)) {
	    ary_double_capa(ary, len);
	}
	rb_mem_clear(RARRAY_PTR(ary) + olen, len - olen);
        ARY_SET_LEN(ary, len);
    }
    else if (ARY_EMBED_P(ary)) {
        ARY_SET_EMBED_LEN(ary, len);
    }
    else if (len <= RARRAY_EMBED_LEN_MAX) {
	VALUE tmp[RARRAY_EMBED_LEN_MAX];
	MEMCPY(tmp, ARY_HEAP_PTR(ary), VALUE, len);
	ary_discard(ary);
	MEMCPY(ARY_EMBED_PTR(ary), tmp, VALUE, len);
        ARY_SET_EMBED_LEN(ary, len);
    }
    else {
	if (olen > len + ARY_DEFAULT_SIZE) {
	    REALLOC_N(RARRAY(ary)->as.heap.ptr, VALUE, len);
	    ARY_SET_CAPA(ary, len);
	}
	ARY_SET_HEAP_LEN(ary, len);
    }
    return ary;
}

/*
 *  call-seq:
 *     ary[index]         = obj                      ->  obj
 *     ary[start, length] = obj or other_ary or nil  ->  obj or other_ary or nil
 *     ary[range]         = obj or other_ary or nil  ->  obj or other_ary or nil
 *
 *  Element Assignment --- Sets the element at +index+, or replaces a subarray
 *  from the +start+ index for +length+ elements, or replaces a subarray
 *  specified by the +range+ of indices.
 *
 *  If indices are greater than the current capacity of the array, the array
 *  grows automatically.  Elements are inserted into the array at +start+ if
 *  +length+ is zero.
 *
 *  Negative indices will count backward from the end of the array.  For
 *  +start+ and +range+ cases the starting index is just before an element.
 *
 *  An IndexError is raised if a negative index points past the beginning of
 *  the array.
 *
 *  See also Array#push, and Array#unshift.
 *
 *     a = Array.new
 *     a[4] = "4";                 #=> [nil, nil, nil, nil, "4"]
 *     a[0, 3] = [ 'a', 'b', 'c' ] #=> ["a", "b", "c", nil, "4"]
 *     a[1..2] = [ 1, 2 ]          #=> ["a", 1, 2, nil, "4"]
 *     a[0, 2] = "?"               #=> ["?", 2, nil, "4"]
 *     a[0..2] = "A"               #=> ["A", "4"]
 *     a[-1]   = "Z"               #=> ["A", "Z"]
 *     a[1..-1] = nil              #=> ["A", nil]
 *     a[1..-1] = []               #=> ["A"]
 *     a[0, 0] = [ 1, 2 ]          #=> [1, 2, "A"]
 *     a[3, 0] = "B"               #=> [1, 2, "A", "B"]
 */

static VALUE
rb_ary_aset(int argc, VALUE *argv, VALUE ary)
{
    long offset, beg, len;

    if (argc == 3) {
	rb_ary_modify_check(ary);
	beg = NUM2LONG(argv[0]);
	len = NUM2LONG(argv[1]);
	rb_ary_splice(ary, beg, len, argv[2]);
	return argv[2];
    }
    rb_check_arity(argc, 2, 2);
    rb_ary_modify_check(ary);
    if (FIXNUM_P(argv[0])) {
	offset = FIX2LONG(argv[0]);
	goto fixnum;
    }
    if (rb_range_beg_len(argv[0], &beg, &len, RARRAY_LEN(ary), 1)) {
	/* check if idx is Range */
	rb_ary_splice(ary, beg, len, argv[1]);
	return argv[1];
    }

    offset = NUM2LONG(argv[0]);
fixnum:
    rb_ary_store(ary, offset, argv[1]);
    return argv[1];
}

/*
 *  call-seq:
 *     ary.insert(index, obj...)  -> ary
 *
 *  Inserts the given values before the element with the given +index+.
 *
 *  Negative indices count backwards from the end of the array, where +-1+ is
 *  the last element.
 *
 *     a = %w{ a b c d }
 *     a.insert(2, 99)         #=> ["a", "b", 99, "c", "d"]
 *     a.insert(-2, 1, 2, 3)   #=> ["a", "b", 99, "c", 1, 2, 3, "d"]
 */

static VALUE
rb_ary_insert(int argc, VALUE *argv, VALUE ary)
{
    long pos;

    rb_check_arity(argc, 1, UNLIMITED_ARGUMENTS);
    rb_ary_modify_check(ary);
    if (argc == 1) return ary;
    pos = NUM2LONG(argv[0]);
    if (pos == -1) {
	pos = RARRAY_LEN(ary);
    }
    if (pos < 0) {
	pos++;
    }
    rb_ary_splice(ary, pos, 0, rb_ary_new4(argc - 1, argv + 1));
    return ary;
}

/*
 *  call-seq:
 *     ary.each { |item| block }  -> ary
 *     ary.each                   -> Enumerator
 *
 *  Calls the given block once for each element in +self+, passing that element
 *  as a parameter.
 *
 *  An Enumerator is returned if no block is given.
 *
 *     a = [ "a", "b", "c" ]
 *     a.each {|x| print x, " -- " }
 *
 *  produces:
 *
 *     a -- b -- c --
 */

VALUE
rb_ary_each(VALUE array)
{
    long i;
    volatile VALUE ary = array;

    RETURN_ENUMERATOR(ary, 0, 0);
    for (i=0; i<RARRAY_LEN(ary); i++) {
	rb_yield(RARRAY_PTR(ary)[i]);
    }
    return ary;
}

/*
 *  call-seq:
 *     ary.each_index { |index| block }  -> ary
 *     ary.each_index                    -> Enumerator
 *
 *  Same as Array#each, but passes the +index+ of the element instead of the
 *  element itself.
 *
 *  An Enumerator is returned if no block is given.
 *
 *     a = [ "a", "b", "c" ]
 *     a.each_index {|x| print x, " -- " }
 *
 *  produces:
 *
 *     0 -- 1 -- 2 --
 */

static VALUE
rb_ary_each_index(VALUE ary)
{
    long i;
    RETURN_ENUMERATOR(ary, 0, 0);

    for (i=0; i<RARRAY_LEN(ary); i++) {
	rb_yield(LONG2NUM(i));
    }
    return ary;
}

/*
 *  call-seq:
 *     ary.reverse_each { |item| block }  -> ary
 *     ary.reverse_each                   -> Enumerator
 *
 *  Same as Array#each, but traverses +self+ in reverse order.
 *
 *     a = [ "a", "b", "c" ]
 *     a.reverse_each {|x| print x, " " }
 *
 *  produces:
 *
 *     c b a
 */

static VALUE
rb_ary_reverse_each(VALUE ary)
{
    long len;

    RETURN_ENUMERATOR(ary, 0, 0);
    len = RARRAY_LEN(ary);
    while (len--) {
	rb_yield(RARRAY_PTR(ary)[len]);
	if (RARRAY_LEN(ary) < len) {
	    len = RARRAY_LEN(ary);
	}
    }
    return ary;
}

/*
 *  call-seq:
 *     ary.length -> int
 *
 *  Returns the number of elements in +self+. May be zero.
 *
 *     [ 1, 2, 3, 4, 5 ].length   #=> 5
 *     [].length                  #=> 0
 */

static VALUE
rb_ary_length(VALUE ary)
{
    long len = RARRAY_LEN(ary);
    return LONG2NUM(len);
}

/*
 *  call-seq:
 *     ary.empty?   -> true or false
 *
 *  Returns +true+ if +self+ contains no elements.
 *
 *     [].empty?   #=> true
 */

static VALUE
rb_ary_empty_p(VALUE ary)
{
    if (RARRAY_LEN(ary) == 0)
	return Qtrue;
    return Qfalse;
}

VALUE
rb_ary_dup(VALUE ary)
{
    VALUE dup = rb_ary_new2(RARRAY_LEN(ary));
    MEMCPY(RARRAY_PTR(dup), RARRAY_PTR(ary), VALUE, RARRAY_LEN(ary));
    ARY_SET_LEN(dup, RARRAY_LEN(ary));
    return dup;
}

VALUE
rb_ary_resurrect(VALUE ary)
{
    return rb_ary_new4(RARRAY_LEN(ary), RARRAY_PTR(ary));
}

extern VALUE rb_output_fs;

static void ary_join_1(VALUE obj, VALUE ary, VALUE sep, long i, VALUE result, int *first);

static VALUE
recursive_join(VALUE obj, VALUE argp, int recur)
{
    VALUE *arg = (VALUE *)argp;
    VALUE ary = arg[0];
    VALUE sep = arg[1];
    VALUE result = arg[2];
    int *first = (int *)arg[3];

    if (recur) {
	rb_raise(rb_eArgError, "recursive array join");
    }
    else {
	ary_join_1(obj, ary, sep, 0, result, first);
    }
    return Qnil;
}

static void
ary_join_0(VALUE ary, VALUE sep, long max, VALUE result)
{
    long i;
    VALUE val;

    if (max > 0) rb_enc_copy(result, RARRAY_PTR(ary)[0]);
    for (i=0; i<max; i++) {
	val = RARRAY_PTR(ary)[i];
	if (i > 0 && !NIL_P(sep))
	    rb_str_buf_append(result, sep);
	rb_str_buf_append(result, val);
	if (OBJ_TAINTED(val)) OBJ_TAINT(result);
	if (OBJ_UNTRUSTED(val)) OBJ_TAINT(result);
    }
}

static void
ary_join_1(VALUE obj, VALUE ary, VALUE sep, long i, VALUE result, int *first)
{
    VALUE val, tmp;

    for (; i<RARRAY_LEN(ary); i++) {
	if (i > 0 && !NIL_P(sep))
	    rb_str_buf_append(result, sep);

	val = RARRAY_PTR(ary)[i];
	switch (TYPE(val)) {
	  case T_STRING:
	  str_join:
	    rb_str_buf_append(result, val);
	    *first = FALSE;
	    break;
	  case T_ARRAY:
	    obj = val;
	  ary_join:
	    if (val == ary) {
		rb_raise(rb_eArgError, "recursive array join");
	    }
	    else {
		VALUE args[4];

		args[0] = val;
		args[1] = sep;
		args[2] = result;
		args[3] = (VALUE)first;
		rb_exec_recursive(recursive_join, obj, (VALUE)args);
	    }
	    break;
	  default:
	    tmp = rb_check_string_type(val);
	    if (!NIL_P(tmp)) {
		val = tmp;
		goto str_join;
	    }
	    tmp = rb_check_convert_type(val, T_ARRAY, "Array", "to_ary");
	    if (!NIL_P(tmp)) {
		obj = val;
		val = tmp;
		goto ary_join;
	    }
	    val = rb_obj_as_string(val);
	    if (*first) {
		rb_enc_copy(result, val);
		*first = FALSE;
	    }
	    goto str_join;
	}
    }
}

VALUE
rb_ary_join(VALUE ary, VALUE sep)
{
    long len = 1, i;
    int taint = FALSE;
    int untrust = FALSE;
    VALUE val, tmp, result;

    if (RARRAY_LEN(ary) == 0) return rb_usascii_str_new(0, 0);
    if (OBJ_TAINTED(ary)) taint = TRUE;
    if (OBJ_UNTRUSTED(ary)) untrust = TRUE;

    if (!NIL_P(sep)) {
	StringValue(sep);
	len += RSTRING_LEN(sep) * (RARRAY_LEN(ary) - 1);
    }
    for (i=0; i<RARRAY_LEN(ary); i++) {
	val = RARRAY_PTR(ary)[i];
	tmp = rb_check_string_type(val);

	if (NIL_P(tmp) || tmp != val) {
	    int first;
	    result = rb_str_buf_new(len + (RARRAY_LEN(ary)-i)*10);
	    rb_enc_associate(result, rb_usascii_encoding());
	    if (taint) OBJ_TAINT(result);
	    if (untrust) OBJ_UNTRUST(result);
	    ary_join_0(ary, sep, i, result);
	    first = i == 0;
	    ary_join_1(ary, ary, sep, i, result, &first);
	    return result;
	}

	len += RSTRING_LEN(tmp);
    }

    result = rb_str_buf_new(len);
    if (taint) OBJ_TAINT(result);
    if (untrust) OBJ_UNTRUST(result);
    ary_join_0(ary, sep, RARRAY_LEN(ary), result);

    return result;
}

/*
 *  call-seq:
 *     ary.join(separator=$,)    -> str
 *
 *  Returns a string created by converting each element of the array to
 *  a string, separated by the given +separator+.
 *  If the +separator+ is +nil+, it uses current $,.
 *  If both the +separator+ and $, are nil, it uses empty string.
 *
 *     [ "a", "b", "c" ].join        #=> "abc"
 *     [ "a", "b", "c" ].join("-")   #=> "a-b-c"
 */

static VALUE
rb_ary_join_m(int argc, VALUE *argv, VALUE ary)
{
    VALUE sep;

    rb_scan_args(argc, argv, "01", &sep);
    if (NIL_P(sep)) sep = rb_output_fs;

    return rb_ary_join(ary, sep);
}

static VALUE
inspect_ary(VALUE ary, VALUE dummy, int recur)
{
    int tainted = OBJ_TAINTED(ary);
    int untrust = OBJ_UNTRUSTED(ary);
    long i;
    VALUE s, str;

    if (recur) return rb_usascii_str_new_cstr("[...]");
    str = rb_str_buf_new2("[");
    for (i=0; i<RARRAY_LEN(ary); i++) {
	s = rb_inspect(RARRAY_PTR(ary)[i]);
	if (OBJ_TAINTED(s)) tainted = TRUE;
	if (OBJ_UNTRUSTED(s)) untrust = TRUE;
	if (i > 0) rb_str_buf_cat2(str, ", ");
	else rb_enc_copy(str, s);
	rb_str_buf_append(str, s);
    }
    rb_str_buf_cat2(str, "]");
    if (tainted) OBJ_TAINT(str);
    if (untrust) OBJ_UNTRUST(str);
    return str;
}

/*
 *  call-seq:
 *     ary.inspect  -> string
 *     ary.to_s     -> string
 *
 *  Creates a string representation of +self+.
 *
 *     [ "a", "b", "c" ].to_s     #=> "[\"a\", \"b\", \"c\"]"
 */

static VALUE
rb_ary_inspect(VALUE ary)
{
    if (RARRAY_LEN(ary) == 0) return rb_usascii_str_new2("[]");
    return rb_exec_recursive(inspect_ary, ary, 0);
}

VALUE
rb_ary_to_s(VALUE ary)
{
    return rb_ary_inspect(ary);
}

/*
 *  call-seq:
 *     ary.to_a     -> ary
 *
 *  Returns +self+.
 *
 *  If called on a subclass of Array, converts the receiver to an Array object.
 */

static VALUE
rb_ary_to_a(VALUE ary)
{
    if (rb_obj_class(ary) != rb_cArray) {
	VALUE dup = rb_ary_new2(RARRAY_LEN(ary));
	rb_ary_replace(dup, ary);
	return dup;
    }
    return ary;
}

/*
 *  call-seq:
 *     ary.to_ary -> ary
 *
 *  Returns +self+.
 */

static VALUE
rb_ary_to_ary_m(VALUE ary)
{
    return ary;
}

static void
ary_reverse(VALUE *p1, VALUE *p2)
{
    while (p1 < p2) {
	VALUE tmp = *p1;
	*p1++ = *p2;
	*p2-- = tmp;
    }
}

VALUE
rb_ary_reverse(VALUE ary)
{
    VALUE *p1, *p2;

    rb_ary_modify(ary);
    if (RARRAY_LEN(ary) > 1) {
	p1 = RARRAY_PTR(ary);
	p2 = p1 + RARRAY_LEN(ary) - 1;	/* points last item */
	ary_reverse(p1, p2);
    }
    return ary;
}

/*
 *  call-seq:
 *     ary.reverse!   -> ary
 *
 *  Reverses +self+ in place.
 *
 *     a = [ "a", "b", "c" ]
 *     a.reverse!       #=> ["c", "b", "a"]
 *     a                #=> ["c", "b", "a"]
 */

static VALUE
rb_ary_reverse_bang(VALUE ary)
{
    return rb_ary_reverse(ary);
}

/*
 *  call-seq:
 *     ary.reverse    -> new_ary
 *
 *  Returns a new array containing +self+'s elements in reverse order.
 *
 *     [ "a", "b", "c" ].reverse   #=> ["c", "b", "a"]
 *     [ 1 ].reverse               #=> [1]
 */

static VALUE
rb_ary_reverse_m(VALUE ary)
{
    long len = RARRAY_LEN(ary);
    VALUE dup = rb_ary_new2(len);

    if (len > 0) {
	VALUE *p1 = RARRAY_PTR(ary);
	VALUE *p2 = RARRAY_PTR(dup) + len - 1;
	do *p2-- = *p1++; while (--len > 0);
    }
    ARY_SET_LEN(dup, RARRAY_LEN(ary));
    return dup;
}

static inline long
rotate_count(long cnt, long len)
{
    return (cnt < 0) ? (len - (~cnt % len) - 1) : (cnt % len);
}

VALUE
rb_ary_rotate(VALUE ary, long cnt)
{
    rb_ary_modify(ary);

    if (cnt != 0) {
	VALUE *ptr = RARRAY_PTR(ary);
	long len = RARRAY_LEN(ary);

	if (len > 0 && (cnt = rotate_count(cnt, len)) > 0) {
	    --len;
	    if (cnt < len) ary_reverse(ptr + cnt, ptr + len);
	    if (--cnt > 0) ary_reverse(ptr, ptr + cnt);
	    if (len > 0) ary_reverse(ptr, ptr + len);
	    return ary;
	}
    }

    return Qnil;
}

/*
 *  call-seq:
 *     ary.rotate!(count=1)   -> ary
 *
 *  Rotates +self+ in place so that the element at +count+ comes first, and
 *  returns +self+.
 *
 *  If +count+ is negative then it rotates in the opposite direction, starting
 *  from the end of the array where +-1+ is the last element.
 *
 *     a = [ "a", "b", "c", "d" ]
 *     a.rotate!        #=> ["b", "c", "d", "a"]
 *     a                #=> ["b", "c", "d", "a"]
 *     a.rotate!(2)     #=> ["d", "a", "b", "c"]
 *     a.rotate!(-3)    #=> ["a", "b", "c", "d"]
 */

static VALUE
rb_ary_rotate_bang(int argc, VALUE *argv, VALUE ary)
{
    long n = 1;

    switch (argc) {
      case 1: n = NUM2LONG(argv[0]);
      case 0: break;
      default: rb_scan_args(argc, argv, "01", NULL);
    }
    rb_ary_rotate(ary, n);
    return ary;
}

/*
 *  call-seq:
 *     ary.rotate(count=1)    -> new_ary
 *
 *  Returns new array by rotating +self+ so that the element at +count+ is the
 *  first element of the new array.
 *
 *  If +count+ is negative then it rotates in the opposite direction, starting
 *  from the end of +self+ where +-1+ is the last element.
 *
 *     a = [ "a", "b", "c", "d" ]
 *     a.rotate         #=> ["b", "c", "d", "a"]
 *     a                #=> ["a", "b", "c", "d"]
 *     a.rotate(2)      #=> ["c", "d", "a", "b"]
 *     a.rotate(-3)     #=> ["b", "c", "d", "a"]
 */

static VALUE
rb_ary_rotate_m(int argc, VALUE *argv, VALUE ary)
{
    VALUE rotated, *ptr, *ptr2;
    long len, cnt = 1;

    switch (argc) {
      case 1: cnt = NUM2LONG(argv[0]);
      case 0: break;
      default: rb_scan_args(argc, argv, "01", NULL);
    }

    len = RARRAY_LEN(ary);
    rotated = rb_ary_new2(len);
    if (len > 0) {
	cnt = rotate_count(cnt, len);
	ptr = RARRAY_PTR(ary);
	ptr2 = RARRAY_PTR(rotated);
	len -= cnt;
	MEMCPY(ptr2, ptr + cnt, VALUE, len);
	MEMCPY(ptr2 + len, ptr, VALUE, cnt);
    }
    ARY_SET_LEN(rotated, RARRAY_LEN(ary));
    return rotated;
}

struct ary_sort_data {
    VALUE ary;
    int opt_methods;
    int opt_inited;
};

enum {
    sort_opt_Fixnum,
    sort_opt_String,
    sort_optimizable_count
};

#define STRING_P(s) (RB_TYPE_P((s), T_STRING) && CLASS_OF(s) == rb_cString)

#define SORT_OPTIMIZABLE_BIT(type) (1U << TOKEN_PASTE(sort_opt_,type))
#define SORT_OPTIMIZABLE(data, type) \
    (((data)->opt_inited & SORT_OPTIMIZABLE_BIT(type)) ? \
     ((data)->opt_methods & SORT_OPTIMIZABLE_BIT(type)) : \
     (((data)->opt_inited |= SORT_OPTIMIZABLE_BIT(type)), \
      rb_method_basic_definition_p(TOKEN_PASTE(rb_c,type), id_cmp) && \
      ((data)->opt_methods |= SORT_OPTIMIZABLE_BIT(type))))

static VALUE
sort_reentered(VALUE ary)
{
    if (RBASIC(ary)->klass) {
	rb_raise(rb_eRuntimeError, "sort reentered");
    }
    return Qnil;
}

static int
sort_1(const void *ap, const void *bp, void *dummy)
{
    struct ary_sort_data *data = dummy;
    VALUE retval = sort_reentered(data->ary);
    VALUE a = *(const VALUE *)ap, b = *(const VALUE *)bp;
    int n;

    retval = rb_yield_values(2, a, b);
    n = rb_cmpint(retval, a, b);
    sort_reentered(data->ary);
    return n;
}

static int
sort_2(const void *ap, const void *bp, void *dummy)
{
    struct ary_sort_data *data = dummy;
    VALUE retval = sort_reentered(data->ary);
    VALUE a = *(const VALUE *)ap, b = *(const VALUE *)bp;
    int n;

    if (FIXNUM_P(a) && FIXNUM_P(b) && SORT_OPTIMIZABLE(data, Fixnum)) {
	if ((long)a > (long)b) return 1;
	if ((long)a < (long)b) return -1;
	return 0;
    }
    if (STRING_P(a) && STRING_P(b) && SORT_OPTIMIZABLE(data, String)) {
	return rb_str_cmp(a, b);
    }

    retval = rb_funcall(a, id_cmp, 1, b);
    n = rb_cmpint(retval, a, b);
    sort_reentered(data->ary);

    return n;
}

/*
 *  call-seq:
 *     ary.sort!                   -> ary
 *     ary.sort! { |a, b| block }  -> ary
 *
 *  Sorts +self+ in place.
 *
 *  Comparisons for the sort will be done using the <code><=></code> operator
 *  or using an optional code block.
 *
 *  The block must implement a comparison between +a+ and +b+, and return
 *  +-1+, when +a+ follows +b+, +0+ when +a+ and +b+ are equivalent, or ++1+
 *  if +b+ follows +a+.
 *
 *  See also Enumerable#sort_by.
 *
 *     a = [ "d", "a", "e", "c", "b" ]
 *     a.sort!                    #=> ["a", "b", "c", "d", "e"]
 *     a.sort! { |x,y| y <=> x }  #=> ["e", "d", "c", "b", "a"]
 */

VALUE
rb_ary_sort_bang(VALUE ary)
{
    rb_ary_modify(ary);
    assert(!ARY_SHARED_P(ary));
    if (RARRAY_LEN(ary) > 1) {
	VALUE tmp = ary_make_substitution(ary); /* only ary refers tmp */
	struct ary_sort_data data;

	RBASIC(tmp)->klass = 0;
	data.ary = tmp;
	data.opt_methods = 0;
	data.opt_inited = 0;
	ruby_qsort(RARRAY_PTR(tmp), RARRAY_LEN(tmp), sizeof(VALUE),
		   rb_block_given_p()?sort_1:sort_2, &data);

        if (ARY_EMBED_P(tmp)) {
            assert(ARY_EMBED_P(tmp));
            if (ARY_SHARED_P(ary)) { /* ary might be destructively operated in the given block */
                rb_ary_unshare(ary);
            }
            FL_SET_EMBED(ary);
            MEMCPY(RARRAY_PTR(ary), ARY_EMBED_PTR(tmp), VALUE, ARY_EMBED_LEN(tmp));
            ARY_SET_LEN(ary, ARY_EMBED_LEN(tmp));
        }
        else {
            assert(!ARY_EMBED_P(tmp));
            if (ARY_HEAP_PTR(ary) == ARY_HEAP_PTR(tmp)) {
                assert(!ARY_EMBED_P(ary));
                FL_UNSET_SHARED(ary);
                ARY_SET_CAPA(ary, ARY_CAPA(tmp));
            }
            else {
                assert(!ARY_SHARED_P(tmp));
                if (ARY_EMBED_P(ary)) {
                    FL_UNSET_EMBED(ary);
                }
                else if (ARY_SHARED_P(ary)) {
                    /* ary might be destructively operated in the given block */
                    rb_ary_unshare(ary);
                }
                else {
                    xfree(ARY_HEAP_PTR(ary));
                }
                ARY_SET_PTR(ary, RARRAY_PTR(tmp));
                ARY_SET_HEAP_LEN(ary, RARRAY_LEN(tmp));
                ARY_SET_CAPA(ary, ARY_CAPA(tmp));
            }
            /* tmp was lost ownership for the ptr */
            FL_UNSET(tmp, FL_FREEZE);
            FL_SET_EMBED(tmp);
            ARY_SET_EMBED_LEN(tmp, 0);
            FL_SET(tmp, FL_FREEZE);
	}
        /* tmp will be GC'ed. */
        RBASIC(tmp)->klass = rb_cArray;
    }
    return ary;
}

/*
 *  call-seq:
 *     ary.sort                   -> new_ary
 *     ary.sort { |a, b| block }  -> new_ary
 *
 *  Returns a new array created by sorting +self+.
 *
 *  Comparisons for the sort will be done using the <code><=></code> operator
 *  or using an optional code block.
 *
 *  The block must implement a comparison between +a+ and +b+, and return
 *  +-1+, when +a+ follows +b+, +0+ when +a+ and +b+ are equivalent, or ++1+
 *  if +b+ follows +a+.
 *
 *
 *  See also Enumerable#sort_by.
 *
 *     a = [ "d", "a", "e", "c", "b" ]
 *     a.sort                    #=> ["a", "b", "c", "d", "e"]
 *     a.sort { |x,y| y <=> x }  #=> ["e", "d", "c", "b", "a"]
 */

VALUE
rb_ary_sort(VALUE ary)
{
    ary = rb_ary_dup(ary);
    rb_ary_sort_bang(ary);
    return ary;
}


static VALUE
sort_by_i(VALUE i)
{
    return rb_yield(i);
}

/*
 *  call-seq:
 *     ary.sort_by! { |obj| block }    -> ary
 *     ary.sort_by!                    -> Enumerator
 *
 *  Sorts +self+ in place using a set of keys generated by mapping the
 *  values in +self+ through the given block.
 *
 *  If no block is given, an Enumerator is returned instead.
 *
 */

static VALUE
rb_ary_sort_by_bang(VALUE ary)
{
    VALUE sorted;

    RETURN_ENUMERATOR(ary, 0, 0);
    rb_ary_modify(ary);
    sorted = rb_block_call(ary, rb_intern("sort_by"), 0, 0, sort_by_i, 0);
    rb_ary_replace(ary, sorted);
    return ary;
}


/*
 *  call-seq:
 *     ary.collect { |item| block }  -> new_ary
 *     ary.map     { |item| block }  -> new_ary
 *     ary.collect                   -> Enumerator
 *     ary.map                       -> Enumerator
 *
 *  Invokes the given block once for each element of +self+.
 *
 *  Creates a new array containing the values returned by the block.
 *
 *  See also Enumerable#collect.
 *
 *  If no block is given, an Enumerator is returned instead.
 *
 *     a = [ "a", "b", "c", "d" ]
 *     a.map { |x| x + "!" }   #=> ["a!", "b!", "c!", "d!"]
 *     a                       #=> ["a", "b", "c", "d"]
 */

static VALUE
rb_ary_collect(VALUE ary)
{
    long i;
    VALUE collect;

    RETURN_ENUMERATOR(ary, 0, 0);
    collect = rb_ary_new2(RARRAY_LEN(ary));
    for (i = 0; i < RARRAY_LEN(ary); i++) {
	rb_ary_push(collect, rb_yield(RARRAY_PTR(ary)[i]));
    }
    return collect;
}


/*
 *  call-seq:
 *     ary.collect! {|item| block }   -> ary
 *     ary.map!     {|item| block }   -> ary
 *     ary.collect!                   -> Enumerator
 *     ary.map!                       -> Enumerator
 *
 *  Invokes the given block once for each element of +self+, replacing the
 *  element with the value returned by the block.
 *
 *  See also Enumerable#collect.
 *
 *  If no block is given, an Enumerator is returned instead.
 *
 *     a = [ "a", "b", "c", "d" ]
 *     a.map! {|x| x + "!" }
 *     a #=>  [ "a!", "b!", "c!", "d!" ]
 */

static VALUE
rb_ary_collect_bang(VALUE ary)
{
    long i;

    RETURN_ENUMERATOR(ary, 0, 0);
    rb_ary_modify(ary);
    for (i = 0; i < RARRAY_LEN(ary); i++) {
	rb_ary_store(ary, i, rb_yield(RARRAY_PTR(ary)[i]));
    }
    return ary;
}

VALUE
rb_get_values_at(VALUE obj, long olen, int argc, VALUE *argv, VALUE (*func) (VALUE, long))
{
    VALUE result = rb_ary_new2(argc);
    long beg, len, i, j;

    for (i=0; i<argc; i++) {
	if (FIXNUM_P(argv[i])) {
	    rb_ary_push(result, (*func)(obj, FIX2LONG(argv[i])));
	    continue;
	}
	/* check if idx is Range */
	if (rb_range_beg_len(argv[i], &beg, &len, olen, 1)) {
	    long end = olen < beg+len ? olen : beg+len;
	    for (j = beg; j < end; j++) {
		rb_ary_push(result, (*func)(obj, j));
	    }
	    if (beg + len > j)
		rb_ary_resize(result, RARRAY_LEN(result) + (beg + len) - j);
	    continue;
	}
	rb_ary_push(result, (*func)(obj, NUM2LONG(argv[i])));
    }
    return result;
}

/*
 *  call-seq:
 *     ary.values_at(selector, ...)  -> new_ary
 *
 *  Returns an array containing the elements in +self+ corresponding to the
 *  given +selector+(s).
 *
 *  The selectors may be either integer indices or ranges.
 *
 *  See also Array#select.
 *
 *     a = %w{ a b c d e f }
 *     a.values_at(1, 3, 5)
 *     a.values_at(1, 3, 5, 7)
 *     a.values_at(-1, -3, -5, -7)
 *     a.values_at(1..3, 2...5)
 */

static VALUE
rb_ary_values_at(int argc, VALUE *argv, VALUE ary)
{
    return rb_get_values_at(ary, RARRAY_LEN(ary), argc, argv, rb_ary_entry);
}


/*
 *  call-seq:
 *     ary.select { |item| block } -> new_ary
 *     ary.select                  -> Enumerator
 *
 *  Returns a new array containing all elements of +ary+
 *  for which the given +block+ returns a true value.
 *
 *  If no block is given, an Enumerator is returned instead.
 *
 *     [1,2,3,4,5].select { |num|  num.even?  }   #=> [2, 4]
 *
 *     a = %w{ a b c d e f }
 *     a.select { |v| v =~ /[aeiou]/ }  #=> ["a", "e"]
 *
 *  See also Enumerable#select.
 */

static VALUE
rb_ary_select(VALUE ary)
{
    VALUE result;
    long i;

    RETURN_ENUMERATOR(ary, 0, 0);
    result = rb_ary_new2(RARRAY_LEN(ary));
    for (i = 0; i < RARRAY_LEN(ary); i++) {
	if (RTEST(rb_yield(RARRAY_PTR(ary)[i]))) {
	    rb_ary_push(result, rb_ary_elt(ary, i));
	}
    }
    return result;
}

/*
 *  call-seq:
 *     ary.select!  {|item| block } -> ary or nil
 *     ary.select!                  -> Enumerator
 *
 *  Invokes the given block passing in successive elements from +self+,
 *  deleting elements for which the block returns a +false+ value.
 *
 *  If changes were made, it will return +self+, otherwise it returns +nil+.
 *
 *  See also Array#keep_if
 *
 *  If no block is given, an Enumerator is returned instead.
 *
 */

static VALUE
rb_ary_select_bang(VALUE ary)
{
    long i1, i2;

    RETURN_ENUMERATOR(ary, 0, 0);
    rb_ary_modify(ary);
    for (i1 = i2 = 0; i1 < RARRAY_LEN(ary); i1++) {
	VALUE v = RARRAY_PTR(ary)[i1];
	if (!RTEST(rb_yield(v))) continue;
	if (i1 != i2) {
	    rb_ary_store(ary, i2, v);
	}
	i2++;
    }

    if (RARRAY_LEN(ary) == i2) return Qnil;
    if (i2 < RARRAY_LEN(ary))
	ARY_SET_LEN(ary, i2);
    return ary;
}

/*
 *  call-seq:
 *     ary.keep_if { |item| block } -> ary
 *     ary.keep_if                  -> Enumerator
 *
 *  Deletes every element of +self+ for which the given block evaluates to
 *  +false+.
 *
 *  See also Array#select!
 *
 *  If no block is given, an Enumerator is returned instead.
 *
 *     a = %w{ a b c d e f }
 *     a.keep_if { |v| v =~ /[aeiou]/ }  #=> ["a", "e"]
 */

static VALUE
rb_ary_keep_if(VALUE ary)
{
    RETURN_ENUMERATOR(ary, 0, 0);
    rb_ary_select_bang(ary);
    return ary;
}

/*
 *  call-seq:
 *     ary.delete(obj)            -> obj or nil
 *     ary.delete(obj) { block }  -> obj or nil
 *
 *  Deletes all items from +self+ that are equal to +obj+.
 *
 *  If any items are found, returns +obj+, otherwise +nil+ is returned instead.
 *
 *  If the optional code block is given, the result of the block is returned if
 *  the item is not found.  (To remove +nil+ elements and get an informative
 *  return value, use Array#compact!)
 *
 *     a = [ "a", "b", "b", "b", "c" ]
 *     a.delete("b")                   #=> "b"
 *     a                               #=> ["a", "c"]
 *     a.delete("z")                   #=> nil
 *     a.delete("z") { "not found" }   #=> "not found"
 */

VALUE
rb_ary_delete(VALUE ary, VALUE item)
{
    VALUE v = item;
    long i1, i2;

    for (i1 = i2 = 0; i1 < RARRAY_LEN(ary); i1++) {
	VALUE e = RARRAY_PTR(ary)[i1];

	if (rb_equal(e, item)) {
	    v = e;
	    continue;
	}
	if (i1 != i2) {
	    rb_ary_store(ary, i2, e);
	}
	i2++;
    }
    if (RARRAY_LEN(ary) == i2) {
	if (rb_block_given_p()) {
	    return rb_yield(item);
	}
	return Qnil;
    }

    rb_ary_modify(ary);
    if (RARRAY_LEN(ary) > i2) {
	ARY_SET_LEN(ary, i2);
	if (i2 * 2 < ARY_CAPA(ary) &&
	    ARY_CAPA(ary) > ARY_DEFAULT_SIZE) {
	    ary_resize_capa(ary, i2*2);
	}
    }

    return v;
}

VALUE
rb_ary_delete_at(VALUE ary, long pos)
{
    long len = RARRAY_LEN(ary);
    VALUE del;

    if (pos >= len) return Qnil;
    if (pos < 0) {
	pos += len;
	if (pos < 0) return Qnil;
    }

    rb_ary_modify(ary);
    del = RARRAY_PTR(ary)[pos];
    MEMMOVE(RARRAY_PTR(ary)+pos, RARRAY_PTR(ary)+pos+1, VALUE,
	    RARRAY_LEN(ary)-pos-1);
    ARY_INCREASE_LEN(ary, -1);

    return del;
}

/*
 *  call-seq:
 *     ary.delete_at(index)  -> obj or nil
 *
 *  Deletes the element at the specified +index+, returning that element, or
 *  +nil+ if the +index+ is out of range.
 *
 *  See also Array#slice!
 *
 *     a = ["ant", "bat", "cat", "dog"]
 *     a.delete_at(2)    #=> "cat"
 *     a                 #=> ["ant", "bat", "dog"]
 *     a.delete_at(99)   #=> nil
 */

static VALUE
rb_ary_delete_at_m(VALUE ary, VALUE pos)
{
    return rb_ary_delete_at(ary, NUM2LONG(pos));
}

/*
 *  call-seq:
 *     ary.slice!(index)         -> obj or nil
 *     ary.slice!(start, length) -> new_ary or nil
 *     ary.slice!(range)         -> new_ary or nil
 *
 *  Deletes the element(s) given by an +index+ (optionally up to +length+
 *  elements) or by a +range+.
 *
 *  Returns the deleted object (or objects), or +nil+ if the +index+ is out of
 *  range.
 *
 *     a = [ "a", "b", "c" ]
 *     a.slice!(1)     #=> "b"
 *     a               #=> ["a", "c"]
 *     a.slice!(-1)    #=> "c"
 *     a               #=> ["a"]
 *     a.slice!(100)   #=> nil
 *     a               #=> ["a"]
 */

static VALUE
rb_ary_slice_bang(int argc, VALUE *argv, VALUE ary)
{
    VALUE arg1, arg2;
    long pos, len, orig_len;

    rb_ary_modify_check(ary);
    if (argc == 2) {
	pos = NUM2LONG(argv[0]);
	len = NUM2LONG(argv[1]);
      delete_pos_len:
	if (len < 0) return Qnil;
	orig_len = RARRAY_LEN(ary);
	if (pos < 0) {
	    pos += orig_len;
	    if (pos < 0) return Qnil;
	}
	else if (orig_len < pos) return Qnil;
	if (orig_len < pos + len) {
	    len = orig_len - pos;
	}
	if (len == 0) return rb_ary_new2(0);
	arg2 = rb_ary_new4(len, RARRAY_PTR(ary)+pos);
	RBASIC(arg2)->klass = rb_obj_class(ary);
	rb_ary_splice(ary, pos, len, Qundef);
	return arg2;
    }

    if (argc != 1) {
	/* error report */
	rb_scan_args(argc, argv, "11", NULL, NULL);
    }
    arg1 = argv[0];

    if (!FIXNUM_P(arg1)) {
	switch (rb_range_beg_len(arg1, &pos, &len, RARRAY_LEN(ary), 0)) {
	  case Qtrue:
	    /* valid range */
	    goto delete_pos_len;
	  case Qnil:
	    /* invalid range */
	    return Qnil;
	  default:
	    /* not a range */
	    break;
	}
    }

    return rb_ary_delete_at(ary, NUM2LONG(arg1));
}

static VALUE
ary_reject(VALUE orig, VALUE result)
{
    long i;

    for (i = 0; i < RARRAY_LEN(orig); i++) {
	VALUE v = RARRAY_PTR(orig)[i];
	if (!RTEST(rb_yield(v))) {
	    rb_ary_push_1(result, v);
	}
    }
    return result;
}

static VALUE
ary_reject_bang(VALUE ary)
{
    long i;
    VALUE result = Qnil;

    rb_ary_modify_check(ary);
    for (i = 0; i < RARRAY_LEN(ary); ) {
	VALUE v = RARRAY_PTR(ary)[i];
	if (RTEST(rb_yield(v))) {
	    rb_ary_delete_at(ary, i);
	    result = ary;
	}
	else {
	    i++;
	}
    }
    return result;
}

/*
 *  call-seq:
 *     ary.reject! { |item| block }  -> ary or nil
 *     ary.reject!                   -> Enumerator
 *
 *  Equivalent to Array#delete_if, deleting elements from +self+ for which the
 *  block evaluates to +true+, but returns +nil+ if no changes were made.
 *
 *  The array is changed instantly every time the block is called, not after
 *  the iteration is over.
 *
 *  See also Enumerable#reject and Array#delete_if.
 *
 *  If no block is given, an Enumerator is returned instead.
 */

static VALUE
rb_ary_reject_bang(VALUE ary)
{
    RETURN_ENUMERATOR(ary, 0, 0);
    return ary_reject_bang(ary);
}

/*
 *  call-seq:
 *     ary.reject  {|item| block }  -> new_ary
 *     ary.reject                   -> Enumerator
 *
 *  Returns a new array containing the items in +self+ for which the given
 *  block is not +true+.
 *
 *  See also Array#delete_if
 *
 *  If no block is given, an Enumerator is returned instead.
 */

static VALUE
rb_ary_reject(VALUE ary)
{
    VALUE rejected_ary;

    RETURN_ENUMERATOR(ary, 0, 0);
    rejected_ary = rb_ary_new();
    ary_reject(ary, rejected_ary);
    return rejected_ary;
}

/*
 *  call-seq:
 *     ary.delete_if { |item| block }  -> ary
 *     ary.delete_if                   -> Enumerator
 *
 *  Deletes every element of +self+ for which block evaluates to +true+.
 *
 *  The array is changed instantly every time the block is called, not after
 *  the iteration is over.
 *
 *  See also Array#reject!
 *
 *  If no block is given, an Enumerator is returned instead.
 *
 *     a = [ "a", "b", "c" ]
 *     a.delete_if {|x| x >= "b" }   #=> ["a"]
 */

static VALUE
rb_ary_delete_if(VALUE ary)
{
    RETURN_ENUMERATOR(ary, 0, 0);
    ary_reject_bang(ary);
    return ary;
}

static VALUE
take_i(VALUE val, VALUE *args, int argc, VALUE *argv)
{
    if (args[1]-- == 0) rb_iter_break();
    if (argc > 1) val = rb_ary_new4(argc, argv);
    rb_ary_push(args[0], val);
    return Qnil;
}

static VALUE
take_items(VALUE obj, long n)
{
    VALUE result = rb_check_array_type(obj);
    VALUE args[2];

    if (!NIL_P(result)) return rb_ary_subseq(result, 0, n);
    result = rb_ary_new2(n);
    args[0] = result; args[1] = (VALUE)n;
    if (rb_check_block_call(obj, rb_intern("each"), 0, 0, take_i, (VALUE)args) == Qundef)
	Check_Type(obj, T_ARRAY);
    return result;
}


/*
 *  call-seq:
 *     ary.zip(arg, ...)                  -> new_ary
 *     ary.zip(arg, ...) { |arr| block }  -> nil
 *
 *  Converts any arguments to arrays, then merges elements of +self+ with
 *  corresponding elements from each argument.
 *
 *  This generates a sequence of <code>ary.size</code> _n_-element arrays,
 *  where _n_ is one more that the count of arguments.
 *
 *  If the size of any argument is less than the size of the initial array,
 *  +nil+ values are supplied.
 *
 *  If a block is given, it is invoked for each output +array+, otherwise an
 *  array of arrays is returned.
 *
 *     a = [ 4, 5, 6 ]
 *     b = [ 7, 8, 9 ]
 *     [1, 2, 3].zip(a, b)   #=> [[1, 4, 7], [2, 5, 8], [3, 6, 9]]
 *     [1, 2].zip(a, b)      #=> [[1, 4, 7], [2, 5, 8]]
 *     a.zip([1, 2], [8])    #=> [[4, 1, 8], [5, 2, nil], [6, nil, nil]]
 */

static VALUE
rb_ary_zip(int argc, VALUE *argv, VALUE ary)
{
    int i, j;
    long len;
    VALUE result = Qnil;

    len = RARRAY_LEN(ary);
    for (i=0; i<argc; i++) {
	argv[i] = take_items(argv[i], len);
    }
    if (!rb_block_given_p()) {
	result = rb_ary_new2(len);
    }

    for (i=0; i<RARRAY_LEN(ary); i++) {
	VALUE tmp = rb_ary_new2(argc+1);

	rb_ary_push(tmp, rb_ary_elt(ary, i));
	for (j=0; j<argc; j++) {
	    rb_ary_push(tmp, rb_ary_elt(argv[j], i));
	}
	if (NIL_P(result)) {
	    rb_yield(tmp);
	}
	else {
	    rb_ary_push(result, tmp);
	}
    }
    return result;
}

/*
 *  call-seq:
 *     ary.transpose -> new_ary
 *
 *  Assumes that +self+ is an array of arrays and transposes the rows and
 *  columns.
 *
 *     a = [[1,2], [3,4], [5,6]]
 *     a.transpose   #=> [[1, 3, 5], [2, 4, 6]]
 *
 *  If the length of the subarrays don't match, an IndexError is raised.
 */

static VALUE
rb_ary_transpose(VALUE ary)
{
    long elen = -1, alen, i, j;
    VALUE tmp, result = 0;

    alen = RARRAY_LEN(ary);
    if (alen == 0) return rb_ary_dup(ary);
    for (i=0; i<alen; i++) {
	tmp = to_ary(rb_ary_elt(ary, i));
	if (elen < 0) {		/* first element */
	    elen = RARRAY_LEN(tmp);
	    result = rb_ary_new2(elen);
	    for (j=0; j<elen; j++) {
		rb_ary_store(result, j, rb_ary_new2(alen));
	    }
	}
	else if (elen != RARRAY_LEN(tmp)) {
	    rb_raise(rb_eIndexError, "element size differs (%ld should be %ld)",
		     RARRAY_LEN(tmp), elen);
	}
	for (j=0; j<elen; j++) {
	    rb_ary_store(rb_ary_elt(result, j), i, rb_ary_elt(tmp, j));
	}
    }
    return result;
}

/*
 *  call-seq:
 *     ary.replace(other_ary)  -> ary
 *
 *  Replaces the contents of +self+ with the contents of +other_ary+,
 *  truncating or expanding if necessary.
 *
 *     a = [ "a", "b", "c", "d", "e" ]
 *     a.replace([ "x", "y", "z" ])   #=> ["x", "y", "z"]
 *     a                              #=> ["x", "y", "z"]
 */

VALUE
rb_ary_replace(VALUE copy, VALUE orig)
{
    rb_ary_modify_check(copy);
    orig = to_ary(orig);
    if (copy == orig) return copy;

    if (RARRAY_LEN(orig) <= RARRAY_EMBED_LEN_MAX) {
        VALUE *ptr;
        VALUE shared = 0;

        if (ARY_OWNS_HEAP_P(copy)) {
            xfree(RARRAY_PTR(copy));
        }
        else if (ARY_SHARED_P(copy)) {
            shared = ARY_SHARED(copy);
            FL_UNSET_SHARED(copy);
        }
        FL_SET_EMBED(copy);
        ptr = RARRAY_PTR(orig);
        MEMCPY(RARRAY_PTR(copy), ptr, VALUE, RARRAY_LEN(orig));
        if (shared) {
            rb_ary_decrement_share(shared);
        }
        ARY_SET_LEN(copy, RARRAY_LEN(orig));
    }
    else {
        VALUE shared = ary_make_shared(orig);
        if (ARY_OWNS_HEAP_P(copy)) {
            xfree(RARRAY_PTR(copy));
        }
        else {
            rb_ary_unshare_safe(copy);
        }
        FL_UNSET_EMBED(copy);
        ARY_SET_PTR(copy, RARRAY_PTR(orig));
        ARY_SET_LEN(copy, RARRAY_LEN(orig));
        rb_ary_set_shared(copy, shared);
    }
    return copy;
}

/*
 *  call-seq:
 *     ary.clear    -> ary
 *
 *  Removes all elements from +self+.
 *
 *     a = [ "a", "b", "c", "d", "e" ]
 *     a.clear    #=> [ ]
 */

VALUE
rb_ary_clear(VALUE ary)
{
    rb_ary_modify_check(ary);
    ARY_SET_LEN(ary, 0);
    if (ARY_SHARED_P(ary)) {
	if (!ARY_EMBED_P(ary)) {
	    rb_ary_unshare(ary);
	    FL_SET_EMBED(ary);
	}
    }
    else if (ARY_DEFAULT_SIZE * 2 < ARY_CAPA(ary)) {
	ary_resize_capa(ary, ARY_DEFAULT_SIZE * 2);
    }
    return ary;
}

/*
 *  call-seq:
 *     ary.fill(obj)                                 -> ary
 *     ary.fill(obj, start [, length])               -> ary
 *     ary.fill(obj, range )                         -> ary
 *     ary.fill { |index| block }                    -> ary
 *     ary.fill(start [, length] ) { |index| block } -> ary
 *     ary.fill(range) { |index| block }             -> ary
 *
 *  The first three forms set the selected elements of +self+ (which
 *  may be the entire array) to +obj+.
 *
 *  A +start+ of +nil+ is equivalent to zero.
 *
 *  A +length+ of +nil+ is equivalent to the length of the array.
 *
 *  The last three forms fill the array with the value of the given block,
 *  which is passed the absolute index of each element to be filled.
 *
 *  Negative values of +start+ count from the end of the array, where +-1+ is
 *  the last element.
 *
 *     a = [ "a", "b", "c", "d" ]
 *     a.fill("x")              #=> ["x", "x", "x", "x"]
 *     a.fill("z", 2, 2)        #=> ["x", "x", "z", "z"]
 *     a.fill("y", 0..1)        #=> ["y", "y", "z", "z"]
 *     a.fill { |i| i*i }       #=> [0, 1, 4, 9]
 *     a.fill(-2) { |i| i*i*i } #=> [0, 1, 8, 27]
 */

static VALUE
rb_ary_fill(int argc, VALUE *argv, VALUE ary)
{
    VALUE item, arg1, arg2;
    long beg = 0, end = 0, len = 0;
    VALUE *p, *pend;
    int block_p = FALSE;

    if (rb_block_given_p()) {
	block_p = TRUE;
	rb_scan_args(argc, argv, "02", &arg1, &arg2);
	argc += 1;		/* hackish */
    }
    else {
	rb_scan_args(argc, argv, "12", &item, &arg1, &arg2);
    }
    switch (argc) {
      case 1:
	beg = 0;
	len = RARRAY_LEN(ary);
	break;
      case 2:
	if (rb_range_beg_len(arg1, &beg, &len, RARRAY_LEN(ary), 1)) {
	    break;
	}
	/* fall through */
      case 3:
	beg = NIL_P(arg1) ? 0 : NUM2LONG(arg1);
	if (beg < 0) {
	    beg = RARRAY_LEN(ary) + beg;
	    if (beg < 0) beg = 0;
	}
	len = NIL_P(arg2) ? RARRAY_LEN(ary) - beg : NUM2LONG(arg2);
	break;
    }
    rb_ary_modify(ary);
    if (len < 0) {
        return ary;
    }
    if (beg >= ARY_MAX_SIZE || len > ARY_MAX_SIZE - beg) {
	rb_raise(rb_eArgError, "argument too big");
    }
    end = beg + len;
    if (RARRAY_LEN(ary) < end) {
	if (end >= ARY_CAPA(ary)) {
	    ary_resize_capa(ary, end);
	}
	rb_mem_clear(RARRAY_PTR(ary) + RARRAY_LEN(ary), end - RARRAY_LEN(ary));
	ARY_SET_LEN(ary, end);
    }

    if (block_p) {
	VALUE v;
	long i;

	for (i=beg; i<end; i++) {
	    v = rb_yield(LONG2NUM(i));
	    if (i>=RARRAY_LEN(ary)) break;
	    RARRAY_PTR(ary)[i] = v;
	}
    }
    else {
	p = RARRAY_PTR(ary) + beg;
	pend = p + len;
	while (p < pend) {
	    *p++ = item;
	}
    }
    return ary;
}

/*
 *  call-seq:
 *     ary + other_ary   -> new_ary
 *
 *  Concatenation --- Returns a new array built by concatenating the
 *  two arrays together to produce a third array.
 *
 *     [ 1, 2, 3 ] + [ 4, 5 ]    #=> [ 1, 2, 3, 4, 5 ]
 *     a = [ "a", "b", "c" ]
 *     a + [ "d", "e", "f" ]
 *     a                         #=> [ "a", "b", "c", "d", "e", "f" ]
 *
 *  See also Array#concat.
 */

VALUE
rb_ary_plus(VALUE x, VALUE y)
{
    VALUE z;
    long len;

    y = to_ary(y);
    len = RARRAY_LEN(x) + RARRAY_LEN(y);
    z = rb_ary_new2(len);
    MEMCPY(RARRAY_PTR(z), RARRAY_PTR(x), VALUE, RARRAY_LEN(x));
    MEMCPY(RARRAY_PTR(z) + RARRAY_LEN(x), RARRAY_PTR(y), VALUE, RARRAY_LEN(y));
    ARY_SET_LEN(z, len);
    return z;
}

/*
 *  call-seq:
 *     ary.concat(other_ary)   -> ary
 *
 *  Appends the elements of +other_ary+ to +self+.
 *
 *     [ "a", "b" ].concat( ["c", "d"] ) #=> [ "a", "b", "c", "d" ]
 *     a = [ 1, 2, 3 ]
 *     a.concat( [ 4, 5 ] )
 *     a                                 #=> [ 1, 2, 3, 4, 5 ]
 *
 *  See also Array#+.
 */

VALUE
rb_ary_concat(VALUE x, VALUE y)
{
    rb_ary_modify_check(x);
    y = to_ary(y);
    if (RARRAY_LEN(y) > 0) {
	rb_ary_splice(x, RARRAY_LEN(x), 0, y);
    }
    return x;
}


/*
 *  call-seq:
 *     ary * int     -> new_ary
 *     ary * str     -> new_string
 *
 *  Repetition --- With a String argument, equivalent to
 *  <code>ary.join(str)</code>.
 *
 *  Otherwise, returns a new array built by concatenating the +int+ copies of
 *  +self+.
 *
 *
 *     [ 1, 2, 3 ] * 3    #=> [ 1, 2, 3, 1, 2, 3, 1, 2, 3 ]
 *     [ 1, 2, 3 ] * ","  #=> "1,2,3"
 *
 */

static VALUE
rb_ary_times(VALUE ary, VALUE times)
{
    VALUE ary2, tmp, *ptr, *ptr2;
    long t, len;

    tmp = rb_check_string_type(times);
    if (!NIL_P(tmp)) {
	return rb_ary_join(ary, tmp);
    }

    len = NUM2LONG(times);
    if (len == 0) {
	ary2 = ary_new(rb_obj_class(ary), 0);
	goto out;
    }
    if (len < 0) {
	rb_raise(rb_eArgError, "negative argument");
    }
    if (ARY_MAX_SIZE/len < RARRAY_LEN(ary)) {
	rb_raise(rb_eArgError, "argument too big");
    }
    len *= RARRAY_LEN(ary);

    ary2 = ary_new(rb_obj_class(ary), len);
    ARY_SET_LEN(ary2, len);

    ptr = RARRAY_PTR(ary);
    ptr2 = RARRAY_PTR(ary2);
    t = RARRAY_LEN(ary);
    if (0 < t) {
        MEMCPY(ptr2, ptr, VALUE, t);
        while (t <= len/2) {
            MEMCPY(ptr2+t, ptr2, VALUE, t);
            t *= 2;
        }
        if (t < len) {
            MEMCPY(ptr2+t, ptr2, VALUE, len-t);
        }
    }
  out:
    OBJ_INFECT(ary2, ary);

    return ary2;
}

/*
 *  call-seq:
 *     ary.assoc(obj)   -> new_ary  or  nil
 *
 *  Searches through an array whose elements are also arrays comparing +obj+
 *  with the first element of each contained array using <code>obj.==</code>.
 *
 *  Returns the first contained array that matches (that is, the first
 *  associated array), or +nil+ if no match is found.
 *
 *  See also Array#rassoc
 *
 *     s1 = [ "colors", "red", "blue", "green" ]
 *     s2 = [ "letters", "a", "b", "c" ]
 *     s3 = "foo"
 *     a  = [ s1, s2, s3 ]
 *     a.assoc("letters")  #=> [ "letters", "a", "b", "c" ]
 *     a.assoc("foo")      #=> nil
 */

VALUE
rb_ary_assoc(VALUE ary, VALUE key)
{
    long i;
    VALUE v;

    for (i = 0; i < RARRAY_LEN(ary); ++i) {
	v = rb_check_array_type(RARRAY_PTR(ary)[i]);
	if (!NIL_P(v) && RARRAY_LEN(v) > 0 &&
	    rb_equal(RARRAY_PTR(v)[0], key))
	    return v;
    }
    return Qnil;
}

/*
 *  call-seq:
 *     ary.rassoc(obj) -> new_ary or nil
 *
 *  Searches through the array whose elements are also arrays.
 *
 *  Compares +obj+ with the second element of each contained array using
 *  <code>obj.==</code>.
 *
 *  Returns the first contained array that matches +obj+.
 *
 *  See also Array#assoc.
 *
 *     a = [ [ 1, "one"], [2, "two"], [3, "three"], ["ii", "two"] ]
 *     a.rassoc("two")    #=> [2, "two"]
 *     a.rassoc("four")   #=> nil
 */

VALUE
rb_ary_rassoc(VALUE ary, VALUE value)
{
    long i;
    VALUE v;

    for (i = 0; i < RARRAY_LEN(ary); ++i) {
	v = RARRAY_PTR(ary)[i];
	if (RB_TYPE_P(v, T_ARRAY) &&
	    RARRAY_LEN(v) > 1 &&
	    rb_equal(RARRAY_PTR(v)[1], value))
	    return v;
    }
    return Qnil;
}

static VALUE
recursive_equal(VALUE ary1, VALUE ary2, int recur)
{
    long i;

    if (recur) return Qtrue; /* Subtle! */
    for (i=0; i<RARRAY_LEN(ary1); i++) {
	if (!rb_equal(rb_ary_elt(ary1, i), rb_ary_elt(ary2, i)))
	    return Qfalse;
    }
    return Qtrue;
}

/*
 *  call-seq:
 *     ary == other_ary   ->   bool
 *
 *  Equality --- Two arrays are equal if they contain the same number of
 *  elements and if each element is equal to (according to Object#==) the
 *  corresponding element in +other_ary+.
 *
 *     [ "a", "c" ]    == [ "a", "c", 7 ]     #=> false
 *     [ "a", "c", 7 ] == [ "a", "c", 7 ]     #=> true
 *     [ "a", "c", 7 ] == [ "a", "d", "f" ]   #=> false
 *
 */

static VALUE
rb_ary_equal(VALUE ary1, VALUE ary2)
{
    if (ary1 == ary2) return Qtrue;
    if (!RB_TYPE_P(ary2, T_ARRAY)) {
	if (!rb_respond_to(ary2, rb_intern("to_ary"))) {
	    return Qfalse;
	}
	return rb_equal(ary2, ary1);
    }
    if (RARRAY_LEN(ary1) != RARRAY_LEN(ary2)) return Qfalse;
    return rb_exec_recursive_paired(recursive_equal, ary1, ary2, ary2);
}

static VALUE
recursive_eql(VALUE ary1, VALUE ary2, int recur)
{
    long i;

    if (recur) return Qtrue; /* Subtle! */
    for (i=0; i<RARRAY_LEN(ary1); i++) {
	if (!rb_eql(rb_ary_elt(ary1, i), rb_ary_elt(ary2, i)))
	    return Qfalse;
    }
    return Qtrue;
}

/*
 *  call-seq:
 *     ary.eql?(other)  -> true or false
 *
 *  Returns +true+ if +self+ and +other+ are the same object,
 *  or are both arrays with the same content.
 */

static VALUE
rb_ary_eql(VALUE ary1, VALUE ary2)
{
    if (ary1 == ary2) return Qtrue;
    if (!RB_TYPE_P(ary2, T_ARRAY)) return Qfalse;
    if (RARRAY_LEN(ary1) != RARRAY_LEN(ary2)) return Qfalse;
    return rb_exec_recursive_paired(recursive_eql, ary1, ary2, ary2);
}

static VALUE
recursive_hash(VALUE ary, VALUE dummy, int recur)
{
    long i;
    st_index_t h;
    VALUE n;

    h = rb_hash_start(RARRAY_LEN(ary));
    if (recur) {
	h = rb_hash_uint(h, NUM2LONG(rb_hash(rb_cArray)));
    }
    else {
	for (i=0; i<RARRAY_LEN(ary); i++) {
	    n = rb_hash(RARRAY_PTR(ary)[i]);
	    h = rb_hash_uint(h, NUM2LONG(n));
	}
    }
    h = rb_hash_end(h);
    return LONG2FIX(h);
}

/*
 *  call-seq:
 *     ary.hash   -> fixnum
 *
 *  Compute a hash-code for this array.
 *
 *  Two arrays with the same content will have the same hash code (and will
 *  compare using #eql?).
 */

static VALUE
rb_ary_hash(VALUE ary)
{
    return rb_exec_recursive_outer(recursive_hash, ary, 0);
}

/*
 *  call-seq:
 *     ary.include?(object)   -> true or false
 *
 *  Returns +true+ if the given +object+ is present in +self+ (that is, if any
 *  object <code>==</code> +object+), otherwise returns +false+.
 *
 *     a = [ "a", "b", "c" ]
 *     a.include?("b")   #=> true
 *     a.include?("z")   #=> false
 */

VALUE
rb_ary_includes(VALUE ary, VALUE item)
{
    long i;

    for (i=0; i<RARRAY_LEN(ary); i++) {
	if (rb_equal(RARRAY_PTR(ary)[i], item)) {
	    return Qtrue;
	}
    }
    return Qfalse;
}


static VALUE
recursive_cmp(VALUE ary1, VALUE ary2, int recur)
{
    long i, len;

    if (recur) return Qundef;	/* Subtle! */
    len = RARRAY_LEN(ary1);
    if (len > RARRAY_LEN(ary2)) {
	len = RARRAY_LEN(ary2);
    }
    for (i=0; i<len; i++) {
	VALUE v = rb_funcall(rb_ary_elt(ary1, i), id_cmp, 1, rb_ary_elt(ary2, i));
	if (v != INT2FIX(0)) {
	    return v;
	}
    }
    return Qundef;
}

/*
 *  call-seq:
 *     ary <=> other_ary   ->  -1, 0, +1 or nil
 *
 *  Comparison --- Returns an integer (+-1+, +0+, or <code>+1</code>) if this
 *  array is less than, equal to, or greater than +other_ary+.
 *
 *  Each object in each array is compared (using the <=> operator).
 *
 *  Arrays are compared in an "element-wise" manner; the first two elements
 *  that are not equal will determine the return value for the whole
 *  comparison.
 *
 *  If all the values are equal, then the return is based on a comparison of
 *  the array lengths. Thus, two arrays are "equal" according to Array#<=> if,
 *  and only if, they have the same length and the value of each element is
 *  equal to the value of the corresponding element in the other array.
 *
 *     [ "a", "a", "c" ]    <=> [ "a", "b", "c" ]   #=> -1
 *     [ 1, 2, 3, 4, 5, 6 ] <=> [ 1, 2 ]            #=> +1
 *
 */

VALUE
rb_ary_cmp(VALUE ary1, VALUE ary2)
{
    long len;
    VALUE v;

    ary2 = rb_check_array_type(ary2);
    if (NIL_P(ary2)) return Qnil;
    if (ary1 == ary2) return INT2FIX(0);
    v = rb_exec_recursive_paired(recursive_cmp, ary1, ary2, ary2);
    if (v != Qundef) return v;
    len = RARRAY_LEN(ary1) - RARRAY_LEN(ary2);
    if (len == 0) return INT2FIX(0);
    if (len > 0) return INT2FIX(1);
    return INT2FIX(-1);
}

static VALUE
ary_add_hash(VALUE hash, VALUE ary)
{
    long i;

    for (i=0; i<RARRAY_LEN(ary); i++) {
	rb_hash_aset(hash, RARRAY_PTR(ary)[i], Qtrue);
    }
    return hash;
}

static inline VALUE
ary_tmp_hash_new(void)
{
    VALUE hash = rb_hash_new();

    RBASIC(hash)->klass = 0;
    return hash;
}

static VALUE
ary_make_hash(VALUE ary)
{
    VALUE hash = ary_tmp_hash_new();
    return ary_add_hash(hash, ary);
}

static VALUE
ary_add_hash_by(VALUE hash, VALUE ary)
{
    long i;

    for (i = 0; i < RARRAY_LEN(ary); ++i) {
	VALUE v = rb_ary_elt(ary, i), k = rb_yield(v);
	if (rb_hash_lookup2(hash, k, Qundef) == Qundef) {
	    rb_hash_aset(hash, k, v);
	}
    }
    return hash;
}

static VALUE
ary_make_hash_by(VALUE ary)
{
    VALUE hash = ary_tmp_hash_new();
    return ary_add_hash_by(hash, ary);
}

static inline void
ary_recycle_hash(VALUE hash)
{
    if (RHASH(hash)->ntbl) {
	st_table *tbl = RHASH(hash)->ntbl;
	RHASH(hash)->ntbl = 0;
	st_free_table(tbl);
    }
}

/*
 *  call-seq:
 *     ary - other_ary    -> new_ary
 *
 *  Array Difference
 *
 *  Returns a new array that is a copy of the original array, removing any
 *  items that also appear in +other_ary+.
 *
 *  It compares elements using their hash (returned by the Object#hash method).
 *
 *     [ 1, 1, 2, 2, 3, 3, 4, 5 ] - [ 1, 2, 4 ]  #=>  [ 3, 3, 5 ]
 *
 *  If you need set-like behavior, see the library class Set.
 */

static VALUE
rb_ary_diff(VALUE ary1, VALUE ary2)
{
    VALUE ary3;
    volatile VALUE hash;
    long i;

    hash = ary_make_hash(to_ary(ary2));
    ary3 = rb_ary_new();

    for (i=0; i<RARRAY_LEN(ary1); i++) {
	if (st_lookup(RHASH_TBL(hash), RARRAY_PTR(ary1)[i], 0)) continue;
	rb_ary_push(ary3, rb_ary_elt(ary1, i));
    }
    ary_recycle_hash(hash);
    return ary3;
}

/*
 *  call-seq:
 *     ary & other_ary      -> new_ary
 *
 *  Set Intersection --- Returns a new array containing elements common to the
 *  two arrays, excluding any duplicates.
 *
 *     [ 1, 1, 3, 5 ] & [ 1, 2, 3 ]                 #=> [ 1, 3 ]
 *     [ 'a', 'b', 'b', 'z' ] & [ 'a', 'b', 'c' ]   #=> [ 'a', 'b' ]
 *
 *  See also Array#uniq.
 */


static VALUE
rb_ary_and(VALUE ary1, VALUE ary2)
{
    VALUE hash, ary3, v;
    st_data_t vv;
    long i;

    ary2 = to_ary(ary2);
    ary3 = rb_ary_new2(RARRAY_LEN(ary1) < RARRAY_LEN(ary2) ?
	    RARRAY_LEN(ary1) : RARRAY_LEN(ary2));
    hash = ary_make_hash(ary2);

    if (RHASH_EMPTY_P(hash))
        return ary3;

    for (i=0; i<RARRAY_LEN(ary1); i++) {
	vv = (st_data_t)(v = rb_ary_elt(ary1, i));
	if (st_delete(RHASH_TBL(hash), &vv, 0)) {
	    rb_ary_push(ary3, v);
	}
    }
    ary_recycle_hash(hash);

    return ary3;
}

/*
 *  call-seq:
 *     ary | other_ary     -> new_ary
 *
 *  Set Union --- Returns a new array by joining +ary+ with +other_ary+,
 *  excluding any duplicates.
 *
 *     [ "a", "b", "c" ] | [ "c", "d", "a" ]    #=> [ "a", "b", "c", "d" ]
 *
 *  See also Array#uniq.
 */

static VALUE
rb_ary_or(VALUE ary1, VALUE ary2)
{
    VALUE hash, ary3, v;
    st_data_t vv;
    long i;

    ary2 = to_ary(ary2);
    ary3 = rb_ary_new2(RARRAY_LEN(ary1)+RARRAY_LEN(ary2));
    hash = ary_add_hash(ary_make_hash(ary1), ary2);

    for (i=0; i<RARRAY_LEN(ary1); i++) {
	vv = (st_data_t)(v = rb_ary_elt(ary1, i));
	if (st_delete(RHASH_TBL(hash), &vv, 0)) {
	    rb_ary_push(ary3, v);
	}
    }
    for (i=0; i<RARRAY_LEN(ary2); i++) {
	vv = (st_data_t)(v = rb_ary_elt(ary2, i));
	if (st_delete(RHASH_TBL(hash), &vv, 0)) {
	    rb_ary_push(ary3, v);
	}
    }
    ary_recycle_hash(hash);
    return ary3;
}

static int
push_value(st_data_t key, st_data_t val, st_data_t ary)
{
    rb_ary_push((VALUE)ary, (VALUE)val);
    return ST_CONTINUE;
}

/*
 *  call-seq:
 *     ary.uniq!                -> ary or nil
 *     ary.uniq! { |item| ... } -> ary or nil
 *
 *  Removes duplicate elements from +self+.
 *
 *  If a block is given, it will use the return value of the block for
 *  comparison.
 *
 *  Returns +nil+ if no changes are made (that is, no duplicates are found).
 *
 *     a = [ "a", "a", "b", "b", "c" ]
 *     a.uniq!   # => ["a", "b", "c"]
 *
 *     b = [ "a", "b", "c" ]
 *     b.uniq!   # => nil
 *
 *     c = [["student","sam"], ["student","george"], ["teacher","matz"]]
 *     c.uniq! { |s| s.first } # => [["student", "sam"], ["teacher", "matz"]]
 *
 */

static VALUE
rb_ary_uniq_bang(VALUE ary)
{
    VALUE hash, v;
    long i, j;

    rb_ary_modify_check(ary);
    if (RARRAY_LEN(ary) <= 1)
        return Qnil;
    if (rb_block_given_p()) {
	hash = ary_make_hash_by(ary);
	if (RARRAY_LEN(ary) == (i = RHASH_SIZE(hash))) {
	    return Qnil;
	}
	ARY_SET_LEN(ary, 0);
	if (ARY_SHARED_P(ary) && !ARY_EMBED_P(ary)) {
	    rb_ary_unshare(ary);
	    FL_SET_EMBED(ary);
	}
	ary_resize_capa(ary, i);
	st_foreach(RHASH_TBL(hash), push_value, ary);
    }
    else {
	hash = ary_make_hash(ary);
	if (RARRAY_LEN(ary) == (long)RHASH_SIZE(hash)) {
	    return Qnil;
	}
	for (i=j=0; i<RARRAY_LEN(ary); i++) {
	    st_data_t vv = (st_data_t)(v = rb_ary_elt(ary, i));
	    if (st_delete(RHASH_TBL(hash), &vv, 0)) {
		rb_ary_store(ary, j++, v);
	    }
	}
	ARY_SET_LEN(ary, j);
    }
    ary_recycle_hash(hash);

    return ary;
}

/*
 *  call-seq:
 *     ary.uniq                -> ary or nil
 *     ary.uniq { |item| ... } -> ary or nil
 *
 *  Returns a new array by removing duplicate values in +self+.
 *
 *  If a block is given, it will use the return value of the block for comparison.
 *
 *  It compares elements using their hash (provided by the Object#hash method)
 *  then compares hashes with Object#eql?.
 *
 *     a = [ "a", "a", "b", "b", "c" ]
 *     a.uniq   # => ["a", "b", "c"]
 *
 *     b = [["student","sam"], ["student","george"], ["teacher","matz"]]
 *     b.uniq { |s| s.first } # => [["student", "sam"], ["teacher", "matz"]]
 *
 */

static VALUE
rb_ary_uniq(VALUE ary)
{
    VALUE hash, uniq, v;
    long i;

    if (RARRAY_LEN(ary) <= 1)
        return rb_ary_dup(ary);
    if (rb_block_given_p()) {
	hash = ary_make_hash_by(ary);
	uniq = ary_new(rb_obj_class(ary), RHASH_SIZE(hash));
	st_foreach(RHASH_TBL(hash), push_value, uniq);
    }
    else {
	hash = ary_make_hash(ary);
	uniq = ary_new(rb_obj_class(ary), RHASH_SIZE(hash));
	for (i=0; i<RARRAY_LEN(ary); i++) {
	    st_data_t vv = (st_data_t)(v = rb_ary_elt(ary, i));
	    if (st_delete(RHASH_TBL(hash), &vv, 0)) {
		rb_ary_push(uniq, v);
	    }
	}
    }
    ary_recycle_hash(hash);

    return uniq;
}

/*
 *  call-seq:
 *     ary.compact!    -> ary  or  nil
 *
 *  Removes +nil+ elements from the array.
 *
 *  Returns +nil+ if no changes were made, otherwise returns the array.
 *
 *     [ "a", nil, "b", nil, "c" ].compact! #=> [ "a", "b", "c" ]
 *     [ "a", "b", "c" ].compact!           #=> nil
 */

static VALUE
rb_ary_compact_bang(VALUE ary)
{
    VALUE *p, *t, *end;
    long n;

    rb_ary_modify(ary);
    p = t = RARRAY_PTR(ary);
    end = p + RARRAY_LEN(ary);

    while (t < end) {
	if (NIL_P(*t)) t++;
	else *p++ = *t++;
    }
    n = p - RARRAY_PTR(ary);
    if (RARRAY_LEN(ary) == n) {
	return Qnil;
    }
    ARY_SET_LEN(ary, n);
    if (n * 2 < ARY_CAPA(ary) && ARY_DEFAULT_SIZE * 2 < ARY_CAPA(ary)) {
	ary_resize_capa(ary, n * 2);
    }

    return ary;
}

/*
 *  call-seq:
 *     ary.compact     -> new_ary
 *
 *  Returns a copy of +self+ with all +nil+ elements removed.
 *
 *     [ "a", nil, "b", nil, "c", nil ].compact
 *                       #=> [ "a", "b", "c" ]
 */

static VALUE
rb_ary_compact(VALUE ary)
{
    ary = rb_ary_dup(ary);
    rb_ary_compact_bang(ary);
    return ary;
}

/*
 *  call-seq:
 *     ary.count                   -> int
 *     ary.count(obj)              -> int
 *     ary.count { |item| block }  -> int
 *
 *  Returns the number of elements.
 *
 *  If an argument is given, counts the number of elements which equal +obj+
 *  using <code>===</code>.
 *
 *  If a block is given, counts the number of elements for which the block
 *  returns a true value.
 *
 *     ary = [1, 2, 4, 2]
 *     ary.count                  #=> 4
 *     ary.count(2)               #=> 2
 *     ary.count { |x| x%2 == 0 } #=> 3
 *
 */

static VALUE
rb_ary_count(int argc, VALUE *argv, VALUE ary)
{
    long n = 0;

    if (argc == 0) {
	VALUE *p, *pend;

	if (!rb_block_given_p())
	    return LONG2NUM(RARRAY_LEN(ary));

	for (p = RARRAY_PTR(ary), pend = p + RARRAY_LEN(ary); p < pend; p++) {
	    if (RTEST(rb_yield(*p))) n++;
	}
    }
    else {
	VALUE obj, *p, *pend;

	rb_scan_args(argc, argv, "1", &obj);
	if (rb_block_given_p()) {
	    rb_warn("given block not used");
	}
	for (p = RARRAY_PTR(ary), pend = p + RARRAY_LEN(ary); p < pend; p++) {
	    if (rb_equal(*p, obj)) n++;
	}
    }

    return LONG2NUM(n);
}

static VALUE
flatten(VALUE ary, int level, int *modified)
{
    long i = 0;
    VALUE stack, result, tmp, elt;
    st_table *memo;
    st_data_t id;

    stack = ary_new(0, ARY_DEFAULT_SIZE);
    result = ary_new(0, RARRAY_LEN(ary));
    memo = st_init_numtable();
    st_insert(memo, (st_data_t)ary, (st_data_t)Qtrue);
    *modified = 0;

    while (1) {
	while (i < RARRAY_LEN(ary)) {
	    elt = RARRAY_PTR(ary)[i++];
	    tmp = rb_check_array_type(elt);
	    if (RBASIC(result)->klass) {
		rb_raise(rb_eRuntimeError, "flatten reentered");
	    }
	    if (NIL_P(tmp) || (level >= 0 && RARRAY_LEN(stack) / 2 >= level)) {
		rb_ary_push(result, elt);
	    }
	    else {
		*modified = 1;
		id = (st_data_t)tmp;
		if (st_lookup(memo, id, 0)) {
		    st_free_table(memo);
		    rb_raise(rb_eArgError, "tried to flatten recursive array");
		}
		st_insert(memo, id, (st_data_t)Qtrue);
		rb_ary_push(stack, ary);
		rb_ary_push(stack, LONG2NUM(i));
		ary = tmp;
		i = 0;
	    }
	}
	if (RARRAY_LEN(stack) == 0) {
	    break;
	}
	id = (st_data_t)ary;
	st_delete(memo, &id, 0);
	tmp = rb_ary_pop(stack);
	i = NUM2LONG(tmp);
	ary = rb_ary_pop(stack);
    }

    st_free_table(memo);

    RBASIC(result)->klass = rb_class_of(ary);
    return result;
}

/*
 *  call-seq:
 *     ary.flatten!        -> Array or nil
 *     ary.flatten!(level) -> Array or nil
 *
 *  Flattens +self+ in place.
 *
 *  Returns +nil+ if no modifications were made (i.e., the array contains no
 *  subarrays.)
 *
 *  The optional +level+ argument determines the level of recursion to flatten.
 *
 *     a = [ 1, 2, [3, [4, 5] ] ]
 *     a.flatten!   #=> [1, 2, 3, 4, 5]
 *     a.flatten!   #=> nil
 *     a            #=> [1, 2, 3, 4, 5]
 *     a = [ 1, 2, [3, [4, 5] ] ]
 *     a.flatten!(1) #=> [1, 2, 3, [4, 5]]
 */

static VALUE
rb_ary_flatten_bang(int argc, VALUE *argv, VALUE ary)
{
    int mod = 0, level = -1;
    VALUE result, lv;

    rb_scan_args(argc, argv, "01", &lv);
    rb_ary_modify_check(ary);
    if (!NIL_P(lv)) level = NUM2INT(lv);
    if (level == 0) return Qnil;

    result = flatten(ary, level, &mod);
    if (mod == 0) {
	ary_discard(result);
	return Qnil;
    }
    if (!(mod = ARY_EMBED_P(result))) rb_obj_freeze(result);
    rb_ary_replace(ary, result);
    if (mod) ARY_SET_EMBED_LEN(result, 0);

    return ary;
}

/*
 *  call-seq:
 *     ary.flatten -> new_ary
 *     ary.flatten(level) -> new_ary
 *
 *  Returns a new array that is a one-dimensional flattening of +self+
 *  (recursively).
 *
 *  That is, for every element that is an array, extract its elements into
 *  the new array.
 *
 *  The optional +level+ argument determines the level of recursion to
 *  flatten.
 *
 *     s = [ 1, 2, 3 ]           #=> [1, 2, 3]
 *     t = [ 4, 5, 6, [7, 8] ]   #=> [4, 5, 6, [7, 8]]
 *     a = [ s, t, 9, 10 ]       #=> [[1, 2, 3], [4, 5, 6, [7, 8]], 9, 10]
 *     a.flatten                 #=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
 *     a = [ 1, 2, [3, [4, 5] ] ]
 *     a.flatten(1)              #=> [1, 2, 3, [4, 5]]
 */

static VALUE
rb_ary_flatten(int argc, VALUE *argv, VALUE ary)
{
    int mod = 0, level = -1;
    VALUE result, lv;

    rb_scan_args(argc, argv, "01", &lv);
    if (!NIL_P(lv)) level = NUM2INT(lv);
    if (level == 0) return ary_make_shared_copy(ary);

    result = flatten(ary, level, &mod);
    OBJ_INFECT(result, ary);

    return result;
}

#define OPTHASH_GIVEN_P(opts) \
    (argc > 0 && !NIL_P((opts) = rb_check_hash_type(argv[argc-1])) && (--argc, 1))
static VALUE sym_random;

#define RAND_UPTO(max) (long)rb_random_ulong_limited((randgen), (max)-1)

/*
 *  call-seq:
 *     ary.shuffle!              -> ary
 *     ary.shuffle!(random: rng) -> ary
 *
 *  Shuffles elements in +self+ in place.
 *
 *  The optional +rng+ argument will be used as random number generator.
 */

static VALUE
rb_ary_shuffle_bang(int argc, VALUE *argv, VALUE ary)
{
    VALUE *ptr, opts, *snap_ptr, randgen = rb_cRandom;
    long i, snap_len;

    if (OPTHASH_GIVEN_P(opts)) {
	randgen = rb_hash_lookup2(opts, sym_random, randgen);
    }
    rb_check_arity(argc, 0, 0);
    rb_ary_modify(ary);
    i = RARRAY_LEN(ary);
    ptr = RARRAY_PTR(ary);
    snap_len = i;
    snap_ptr = ptr;
    while (i) {
	long j = RAND_UPTO(i);
	VALUE tmp;
	if (snap_len != RARRAY_LEN(ary) || snap_ptr != RARRAY_PTR(ary)) {
	    rb_raise(rb_eRuntimeError, "modified during shuffle");
	}
	tmp = ptr[--i];
	ptr[i] = ptr[j];
	ptr[j] = tmp;
    }
    return ary;
}


/*
 *  call-seq:
 *     ary.shuffle              -> new_ary
 *     ary.shuffle(random: rng) -> new_ary
 *
 *  Returns a new array with elements of +self+ shuffled.
 *
 *     a = [ 1, 2, 3 ]           #=> [1, 2, 3]
 *     a.shuffle                 #=> [2, 3, 1]
 *
 *  The optional +rng+ argument will be used as the random number generator.
 *
 *     a.shuffle(random: Random.new(1))  #=> [1, 3, 2]
 */

static VALUE
rb_ary_shuffle(int argc, VALUE *argv, VALUE ary)
{
    ary = rb_ary_dup(ary);
    rb_ary_shuffle_bang(argc, argv, ary);
    return ary;
}


/*
 *  call-seq:
 *     ary.sample                  -> obj
 *     ary.sample(random: rng)     -> obj
 *     ary.sample(n)               -> new_ary
 *     ary.sample(n, random: rng)  -> new_ary
 *
 *  Choose a random element or +n+ random elements from the array.
 *
 *  The elements are chosen by using random and unique indices into the array
 *  in order to ensure that an element doesn't repeat itself unless the array
 *  already contained duplicate elements.
 *
 *  If the array is empty the first form returns +nil+ and the second form
 *  returns an empty array.
 *
 *  The optional +rng+ argument will be used as the random number generator.
 *
 *     a = [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ]
 *     a.sample         #=> 7
 *     a.sample(4)      #=> [6, 4, 2, 5]
 */


static VALUE
rb_ary_sample(int argc, VALUE *argv, VALUE ary)
{
    VALUE nv, result, *ptr;
    VALUE opts, randgen = rb_cRandom;
    long n, len, i, j, k, idx[10];
    long rnds[numberof(idx)];

    if (OPTHASH_GIVEN_P(opts)) {
	randgen = rb_hash_lookup2(opts, sym_random, randgen);
    }
    ptr = RARRAY_PTR(ary);
    len = RARRAY_LEN(ary);
    if (argc == 0) {
	if (len == 0) return Qnil;
	if (len == 1) {
	    i = 0;
	}
	else {
	    i = RAND_UPTO(len);
	    if ((len = RARRAY_LEN(ary)) <= i) return Qnil;
	    ptr = RARRAY_PTR(ary);
	}
	return ptr[i];
    }
    rb_scan_args(argc, argv, "1", &nv);
    n = NUM2LONG(nv);
    if (n < 0) rb_raise(rb_eArgError, "negative sample number");
    if (n > len) n = len;
    if (n <= numberof(idx)) {
	for (i = 0; i < n; ++i) {
	    rnds[i] = RAND_UPTO(len - i);
	}
    }
    k = len;
    len = RARRAY_LEN(ary);
    ptr = RARRAY_PTR(ary);
    if (len < k) {
	if (n <= numberof(idx)) {
	    for (i = 0; i < n; ++i) {
		if (rnds[i] >= len) {
		    return rb_ary_new2(0);
		}
	    }
	}
    }
    if (n > len) n = len;
    switch (n) {
      case 0:
	return rb_ary_new2(0);
      case 1:
	i = rnds[0];
	return rb_ary_new4(1, &ptr[i]);
      case 2:
	i = rnds[0];
	j = rnds[1];
	if (j >= i) j++;
	return rb_ary_new3(2, ptr[i], ptr[j]);
      case 3:
	i = rnds[0];
	j = rnds[1];
	k = rnds[2];
	{
	    long l = j, g = i;
	    if (j >= i) l = i, g = ++j;
	    if (k >= l && (++k >= g)) ++k;
	}
	return rb_ary_new3(3, ptr[i], ptr[j], ptr[k]);
    }
    if (n <= numberof(idx)) {
	VALUE *ptr_result;
	long sorted[numberof(idx)];
	sorted[0] = idx[0] = rnds[0];
	for (i=1; i<n; i++) {
	    k = rnds[i];
	    for (j = 0; j < i; ++j) {
		if (k < sorted[j]) break;
		++k;
	    }
	    memmove(&sorted[j+1], &sorted[j], sizeof(sorted[0])*(i-j));
	    sorted[j] = idx[i] = k;
	}
	result = rb_ary_new2(n);
	ptr_result = RARRAY_PTR(result);
	for (i=0; i<n; i++) {
	    ptr_result[i] = ptr[idx[i]];
	}
    }
    else {
	VALUE *ptr_result;
	result = rb_ary_new4(len, ptr);
	RBASIC(result)->klass = 0;
	ptr_result = RARRAY_PTR(result);
	RB_GC_GUARD(ary);
	for (i=0; i<n; i++) {
	    j = RAND_UPTO(len-i) + i;
	    nv = ptr_result[j];
	    ptr_result[j] = ptr_result[i];
	    ptr_result[i] = nv;
	}
	RBASIC(result)->klass = rb_cArray;
    }
    ARY_SET_LEN(result, n);

    return result;
}


/*
 *  call-seq:
 *     ary.cycle(n=nil) { |obj| block }  -> nil
 *     ary.cycle(n=nil)                  -> Enumerator
 *
 *  Calls the given block for each element +n+ times or forever if +nil+ is
 *  given.
 *
 *  Does nothing if a non-positive number is given or the array is empty.
 *
 *  Returns +nil+ if the loop has finished without getting interrupted.
 *
 *  If no block is given, an Enumerator is returned instead.
 *
 *     a = ["a", "b", "c"]
 *     a.cycle { |x| puts x }     # print, a, b, c, a, b, c,.. forever.
 *     a.cycle(2) { |x| puts x }  # print, a, b, c, a, b, c.
 *
 */

static VALUE
rb_ary_cycle(int argc, VALUE *argv, VALUE ary)
{
    long n, i;
    VALUE nv = Qnil;

    rb_scan_args(argc, argv, "01", &nv);

    RETURN_ENUMERATOR(ary, argc, argv);
    if (NIL_P(nv)) {
        n = -1;
    }
    else {
        n = NUM2LONG(nv);
        if (n <= 0) return Qnil;
    }

    while (RARRAY_LEN(ary) > 0 && (n < 0 || 0 < n--)) {
        for (i=0; i<RARRAY_LEN(ary); i++) {
            rb_yield(RARRAY_PTR(ary)[i]);
        }
    }
    return Qnil;
}

#define tmpbuf(n, size) rb_str_tmp_new((n)*(size))
#define tmpbuf_discard(s) (rb_str_resize((s), 0L), RBASIC(s)->klass = rb_cString)
#define tmpary(n) rb_ary_tmp_new(n)
#define tmpary_discard(a) (ary_discard(a), RBASIC(a)->klass = rb_cArray)

/*
 * Recursively compute permutations of +r+ elements of the set
 * <code>[0..n-1]</code>.
 *
 * When we have a complete permutation of array indexes, copy the values
 * at those indexes into a new array and yield that array.
 *
 * n: the size of the set
 * r: the number of elements in each permutation
 * p: the array (of size r) that we're filling in
 * index: what index we're filling in now
 * used: an array of booleans: whether a given index is already used
 * values: the Ruby array that holds the actual values to permute
 */
static void
permute0(long n, long r, long *p, long index, char *used, VALUE values)
{
    long i,j;
    for (i = 0; i < n; i++) {
	if (used[i] == 0) {
	    p[index] = i;
	    if (index < r-1) {             /* if not done yet */
		used[i] = 1;               /* mark index used */
		permute0(n, r, p, index+1, /* recurse */
			 used, values);
		used[i] = 0;               /* index unused */
	    }
	    else {
		/* We have a complete permutation of array indexes */
		/* Build a ruby array of the corresponding values */
		/* And yield it to the associated block */
		VALUE result = rb_ary_new2(r);
		VALUE *result_array = RARRAY_PTR(result);
		const VALUE *values_array = RARRAY_PTR(values);

		for (j = 0; j < r; j++) result_array[j] = values_array[p[j]];
		ARY_SET_LEN(result, r);
		rb_yield(result);
		if (RBASIC(values)->klass) {
		    rb_raise(rb_eRuntimeError, "permute reentered");
		}
	    }
	}
    }
}

/*
 *  call-seq:
 *     ary.permutation { |p| block }          -> ary
 *     ary.permutation                        -> Enumerator
 *     ary.permutation(n) { |p| block }       -> ary
 *     ary.permutation(n)                     -> Enumerator
 *
 * When invoked with a block, yield all permutations of length +n+ of the
 * elements of the array, then return the array itself.
 *
 * If +n+ is not specified, yield all permutations of all elements.
 *
 * The implementation makes no guarantees about the order in which the
 * permutations are yielded.
 *
 * If no block is given, an Enumerator is returned instead.
 *
 * Examples:
 *
 *   a = [1, 2, 3]
 *   a.permutation.to_a    #=> [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]
 *   a.permutation(1).to_a #=> [[1],[2],[3]]
 *   a.permutation(2).to_a #=> [[1,2],[1,3],[2,1],[2,3],[3,1],[3,2]]
 *   a.permutation(3).to_a #=> [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]
 *   a.permutation(0).to_a #=> [[]] # one permutation of length 0
 *   a.permutation(4).to_a #=> []   # no permutations of length 4
 */

static VALUE
rb_ary_permutation(int argc, VALUE *argv, VALUE ary)
{
    VALUE num;
    long r, n, i;

    n = RARRAY_LEN(ary);                  /* Array length */
    RETURN_ENUMERATOR(ary, argc, argv);   /* Return Enumerator if no block */
    rb_scan_args(argc, argv, "01", &num);
    r = NIL_P(num) ? n : NUM2LONG(num);   /* Permutation size from argument */

    if (r < 0 || n < r) {
	/* no permutations: yield nothing */
    }
    else if (r == 0) { /* exactly one permutation: the zero-length array */
	rb_yield(rb_ary_new2(0));
    }
    else if (r == 1) { /* this is a special, easy case */
	for (i = 0; i < RARRAY_LEN(ary); i++) {
	    rb_yield(rb_ary_new3(1, RARRAY_PTR(ary)[i]));
	}
    }
    else {             /* this is the general case */
	volatile VALUE t0 = tmpbuf(n,sizeof(long));
	long *p = (long*)RSTRING_PTR(t0);
	volatile VALUE t1 = tmpbuf(n,sizeof(char));
	char *used = (char*)RSTRING_PTR(t1);
	VALUE ary0 = ary_make_shared_copy(ary); /* private defensive copy of ary */
	RBASIC(ary0)->klass = 0;

	MEMZERO(used, char, n); /* initialize array */

	permute0(n, r, p, 0, used, ary0); /* compute and yield permutations */
	tmpbuf_discard(t0);
	tmpbuf_discard(t1);
	RBASIC(ary0)->klass = rb_cArray;
    }
    return ary;
}

/*
 *  call-seq:
 *     ary.combination(n) { |c| block }    -> ary
 *     ary.combination(n)                  -> Enumerator
 *
 * When invoked with a block, yields all combinations of length +n+ of elements
 * from the array and then returns the array itself.
 *
 * The implementation makes no guarantees about the order in which the
 * combinations are yielded.
 *
 * If no block is given, an Enumerator is returned instead.
 *
 * Examples:
 *
 *     a = [1, 2, 3, 4]
 *     a.combination(1).to_a  #=> [[1],[2],[3],[4]]
 *     a.combination(2).to_a  #=> [[1,2],[1,3],[1,4],[2,3],[2,4],[3,4]]
 *     a.combination(3).to_a  #=> [[1,2,3],[1,2,4],[1,3,4],[2,3,4]]
 *     a.combination(4).to_a  #=> [[1,2,3,4]]
 *     a.combination(0).to_a  #=> [[]] # one combination of length 0
 *     a.combination(5).to_a  #=> []   # no combinations of length 5
 *
 */

static VALUE
rb_ary_combination(VALUE ary, VALUE num)
{
    long n, i, len;

    n = NUM2LONG(num);
    RETURN_ENUMERATOR(ary, 1, &num);
    len = RARRAY_LEN(ary);
    if (n < 0 || len < n) {
	/* yield nothing */
    }
    else if (n == 0) {
	rb_yield(rb_ary_new2(0));
    }
    else if (n == 1) {
	for (i = 0; i < len; i++) {
	    rb_yield(rb_ary_new3(1, RARRAY_PTR(ary)[i]));
	}
    }
    else {
	volatile VALUE t0 = tmpbuf(n+1, sizeof(long));
	long *stack = (long*)RSTRING_PTR(t0);
	volatile VALUE cc = tmpary(n);
	VALUE *chosen = RARRAY_PTR(cc);
	long lev = 0;

	MEMZERO(stack, long, n);
	stack[0] = -1;
	for (;;) {
	    chosen[lev] = RARRAY_PTR(ary)[stack[lev+1]];
	    for (lev++; lev < n; lev++) {
		chosen[lev] = RARRAY_PTR(ary)[stack[lev+1] = stack[lev]+1];
	    }
	    rb_yield(rb_ary_new4(n, chosen));
	    if (RBASIC(t0)->klass) {
		rb_raise(rb_eRuntimeError, "combination reentered");
	    }
	    do {
		if (lev == 0) goto done;
		stack[lev--]++;
	    } while (stack[lev+1]+n == len+lev+1);
	}
    done:
	tmpbuf_discard(t0);
	tmpary_discard(cc);
    }
    return ary;
}

/*
 * Recursively compute repeated permutations of +r+ elements of the set
 * <code>[0..n-1]</code>.
 *
 * When we have a complete repeated permutation of array indexes, copy the
 * values at those indexes into a new array and yield that array.
 *
 * n: the size of the set
 * r: the number of elements in each permutation
 * p: the array (of size r) that we're filling in
 * index: what index we're filling in now
 * values: the Ruby array that holds the actual values to permute
 */
static void
rpermute0(long n, long r, long *p, long index, VALUE values)
{
    long i, j;
    for (i = 0; i < n; i++) {
	p[index] = i;
	if (index < r-1) {              /* if not done yet */
	    rpermute0(n, r, p, index+1, values); /* recurse */
	}
	else {
	    /* We have a complete permutation of array indexes */
	    /* Build a ruby array of the corresponding values */
	    /* And yield it to the associated block */
	    VALUE result = rb_ary_new2(r);
	    VALUE *result_array = RARRAY_PTR(result);
	    const VALUE *values_array = RARRAY_PTR(values);

	    for (j = 0; j < r; j++) result_array[j] = values_array[p[j]];
	    ARY_SET_LEN(result, r);
	    rb_yield(result);
	    if (RBASIC(values)->klass) {
		rb_raise(rb_eRuntimeError, "repeated permute reentered");
	    }
	}
    }
}

/*
 *  call-seq:
 *     ary.repeated_permutation(n) { |p| block } -> ary
 *     ary.repeated_permutation(n)               -> Enumerator
 *
 * When invoked with a block, yield all repeated permutations of length +n+ of
 * the elements of the array, then return the array itself.
 *
 * The implementation makes no guarantees about the order in which the repeated
 * permutations are yielded.
 *
 * If no block is given, an Enumerator is returned instead.
 *
 * Examples:
 *
 *     a = [1, 2]
 *     a.repeated_permutation(1).to_a  #=> [[1], [2]]
 *     a.repeated_permutation(2).to_a  #=> [[1,1],[1,2],[2,1],[2,2]]
 *     a.repeated_permutation(3).to_a  #=> [[1,1,1],[1,1,2],[1,2,1],[1,2,2],
 *                                     #    [2,1,1],[2,1,2],[2,2,1],[2,2,2]]
 *     a.repeated_permutation(0).to_a  #=> [[]] # one permutation of length 0
 */

static VALUE
rb_ary_repeated_permutation(VALUE ary, VALUE num)
{
    long r, n, i;

    n = RARRAY_LEN(ary);                  /* Array length */
    RETURN_ENUMERATOR(ary, 1, &num);      /* Return Enumerator if no block */
    r = NUM2LONG(num);                    /* Permutation size from argument */

    if (r < 0) {
	/* no permutations: yield nothing */
    }
    else if (r == 0) { /* exactly one permutation: the zero-length array */
	rb_yield(rb_ary_new2(0));
    }
    else if (r == 1) { /* this is a special, easy case */
	for (i = 0; i < RARRAY_LEN(ary); i++) {
	    rb_yield(rb_ary_new3(1, RARRAY_PTR(ary)[i]));
	}
    }
    else {             /* this is the general case */
	volatile VALUE t0 = tmpbuf(r, sizeof(long));
	long *p = (long*)RSTRING_PTR(t0);
	VALUE ary0 = ary_make_shared_copy(ary); /* private defensive copy of ary */
	RBASIC(ary0)->klass = 0;

	rpermute0(n, r, p, 0, ary0); /* compute and yield repeated permutations */
	tmpbuf_discard(t0);
	RBASIC(ary0)->klass = rb_cArray;
    }
    return ary;
}

static void
rcombinate0(long n, long r, long *p, long index, long rest, VALUE values)
{
    long j;
    if (rest > 0) {
	for (; index < n; ++index) {
	    p[r-rest] = index;
	    rcombinate0(n, r, p, index, rest-1, values);
	}
    }
    else {
	VALUE result = rb_ary_new2(r);
	VALUE *result_array = RARRAY_PTR(result);
	const VALUE *values_array = RARRAY_PTR(values);

	for (j = 0; j < r; ++j) result_array[j] = values_array[p[j]];
	ARY_SET_LEN(result, r);
	rb_yield(result);
	if (RBASIC(values)->klass) {
	    rb_raise(rb_eRuntimeError, "repeated combination reentered");
	}
    }
}

/*
 *  call-seq:
 *     ary.repeated_combination(n) { |c| block } -> ary
 *     ary.repeated_combination(n)               -> Enumerator
 *
 * When invoked with a block, yields all repeated combinations of length +n+ of
 * elements from the array and then returns the array itself.
 *
 * The implementation makes no guarantees about the order in which the repeated
 * combinations are yielded.
 *
 * If no block is given, an Enumerator is returned instead.
 *
 * Examples:
 *
 *   a = [1, 2, 3]
 *   a.repeated_combination(1).to_a  #=> [[1], [2], [3]]
 *   a.repeated_combination(2).to_a  #=> [[1,1],[1,2],[1,3],[2,2],[2,3],[3,3]]
 *   a.repeated_combination(3).to_a  #=> [[1,1,1],[1,1,2],[1,1,3],[1,2,2],[1,2,3],
 *                                   #    [1,3,3],[2,2,2],[2,2,3],[2,3,3],[3,3,3]]
 *   a.repeated_combination(4).to_a  #=> [[1,1,1,1],[1,1,1,2],[1,1,1,3],[1,1,2,2],[1,1,2,3],
 *                                   #    [1,1,3,3],[1,2,2,2],[1,2,2,3],[1,2,3,3],[1,3,3,3],
 *                                   #    [2,2,2,2],[2,2,2,3],[2,2,3,3],[2,3,3,3],[3,3,3,3]]
 *   a.repeated_combination(0).to_a  #=> [[]] # one combination of length 0
 *
 */

static VALUE
rb_ary_repeated_combination(VALUE ary, VALUE num)
{
    long n, i, len;

    n = NUM2LONG(num);                 /* Combination size from argument */
    RETURN_ENUMERATOR(ary, 1, &num);   /* Return Enumerator if no block */
    len = RARRAY_LEN(ary);
    if (n < 0) {
	/* yield nothing */
    }
    else if (n == 0) {
	rb_yield(rb_ary_new2(0));
    }
    else if (n == 1) {
	for (i = 0; i < len; i++) {
	    rb_yield(rb_ary_new3(1, RARRAY_PTR(ary)[i]));
	}
    }
    else if (len == 0) {
	/* yield nothing */
    }
    else {
	volatile VALUE t0 = tmpbuf(n, sizeof(long));
	long *p = (long*)RSTRING_PTR(t0);
	VALUE ary0 = ary_make_shared_copy(ary); /* private defensive copy of ary */
	RBASIC(ary0)->klass = 0;

	rcombinate0(len, n, p, 0, n, ary0); /* compute and yield repeated combinations */
	tmpbuf_discard(t0);
	RBASIC(ary0)->klass = rb_cArray;
    }
    return ary;
}

/*
 *  call-seq:
 *     ary.product(other_ary, ...)                -> new_ary
 *     ary.product(other_ary, ...) { |p| block }  -> ary
 *
 *  Returns an array of all combinations of elements from all arrays.
 *
 *  The length of the returned array is the product of the length of +self+ and
 *  the argument arrays.
 *
 *  If given a block, #product will yield all combinations and return +self+
 *  instead.
 *
 *     [1,2,3].product([4,5])     #=> [[1,4],[1,5],[2,4],[2,5],[3,4],[3,5]]
 *     [1,2].product([1,2])       #=> [[1,1],[1,2],[2,1],[2,2]]
 *     [1,2].product([3,4],[5,6]) #=> [[1,3,5],[1,3,6],[1,4,5],[1,4,6],
 *                                #     [2,3,5],[2,3,6],[2,4,5],[2,4,6]]
 *     [1,2].product()            #=> [[1],[2]]
 *     [1,2].product([])          #=> []
 */

static VALUE
rb_ary_product(int argc, VALUE *argv, VALUE ary)
{
    int n = argc+1;    /* How many arrays we're operating on */
    volatile VALUE t0 = tmpary(n);
    volatile VALUE t1 = tmpbuf(n, sizeof(int));
    VALUE *arrays = RARRAY_PTR(t0); /* The arrays we're computing the product of */
    int *counters = (int*)RSTRING_PTR(t1); /* The current position in each one */
    VALUE result = Qnil;      /* The array we'll be returning, when no block given */
    long i,j;
    long resultlen = 1;

    RBASIC(t0)->klass = 0;
    RBASIC(t1)->klass = 0;

    /* initialize the arrays of arrays */
    ARY_SET_LEN(t0, n);
    arrays[0] = ary;
    for (i = 1; i < n; i++) arrays[i] = Qnil;
    for (i = 1; i < n; i++) arrays[i] = to_ary(argv[i-1]);

    /* initialize the counters for the arrays */
    for (i = 0; i < n; i++) counters[i] = 0;

    /* Otherwise, allocate and fill in an array of results */
    if (rb_block_given_p()) {
	/* Make defensive copies of arrays; exit if any is empty */
	for (i = 0; i < n; i++) {
	    if (RARRAY_LEN(arrays[i]) == 0) goto done;
	    arrays[i] = ary_make_shared_copy(arrays[i]);
	}
    }
    else {
	/* Compute the length of the result array; return [] if any is empty */
	for (i = 0; i < n; i++) {
	    long k = RARRAY_LEN(arrays[i]), l = resultlen;
	    if (k == 0) {
		result = rb_ary_new2(0);
		goto done;
	    }
	    resultlen *= k;
	    if (resultlen < k || resultlen < l || resultlen / k != l) {
		rb_raise(rb_eRangeError, "too big to product");
	    }
	}
	result = rb_ary_new2(resultlen);
    }
    for (;;) {
	int m;
	/* fill in one subarray */
	VALUE subarray = rb_ary_new2(n);
	for (j = 0; j < n; j++) {
	    rb_ary_push(subarray, rb_ary_entry(arrays[j], counters[j]));
	}

	/* put it on the result array */
	if(NIL_P(result)) {
	    FL_SET(t0, FL_USER5);
	    rb_yield(subarray);
	    if (! FL_TEST(t0, FL_USER5)) {
		rb_raise(rb_eRuntimeError, "product reentered");
	    }
	    else {
		FL_UNSET(t0, FL_USER5);
	    }
	}
	else {
	    rb_ary_push(result, subarray);
	}

	/*
	 * Increment the last counter.  If it overflows, reset to 0
	 * and increment the one before it.
	 */
	m = n-1;
	counters[m]++;
	while (counters[m] == RARRAY_LEN(arrays[m])) {
	    counters[m] = 0;
	    /* If the first counter overflows, we are done */
	    if (--m < 0) goto done;
	    counters[m]++;
	}
    }
done:
    tmpary_discard(t0);
    tmpbuf_discard(t1);

    return NIL_P(result) ? ary : result;
}

/*
 *  call-seq:
 *     ary.take(n)               -> new_ary
 *
 *  Returns first +n+ elements from the array.
 *
 *  If a non-positive number is given, raises an ArgumentError.
 *
 *  See also Array#drop
 *
 *     a = [1, 2, 3, 4, 5, 0]
 *     a.take(3)             #=> [1, 2, 3]
 *
 */

static VALUE
rb_ary_take(VALUE obj, VALUE n)
{
    long len = NUM2LONG(n);
    if (len < 0) {
	rb_raise(rb_eArgError, "attempt to take negative size");
    }
    return rb_ary_subseq(obj, 0, len);
}

/*
 *  call-seq:
 *     ary.take_while { |arr| block }  -> new_ary
 *     ary.take_while                  -> Enumerator
 *
 *  Passes elements to the block until the block returns +nil+ or +false+, then
 *  stops iterating and returns an array of all prior elements.
 *
 *  If no block is given, an Enumerator is returned instead.
 *
 *  See also Array#drop_while
 *
 *     a = [1, 2, 3, 4, 5, 0]
 *     a.take_while { |i| i < 3 }  #=> [1, 2]
 *
 */

static VALUE
rb_ary_take_while(VALUE ary)
{
    long i;

    RETURN_ENUMERATOR(ary, 0, 0);
    for (i = 0; i < RARRAY_LEN(ary); i++) {
	if (!RTEST(rb_yield(RARRAY_PTR(ary)[i]))) break;
    }
    return rb_ary_take(ary, LONG2FIX(i));
}

/*
 *  call-seq:
 *     ary.drop(n)               -> new_ary
 *
 *  Drops first +n+ elements from +ary+ and returns the rest of the elements in
 *  an array.
 *
 *  If a non-positive number is given, raises an ArgumentError.
 *
 *  See also Array#take
 *
 *     a = [1, 2, 3, 4, 5, 0]
 *     a.drop(3)             #=> [4, 5, 0]
 *
 */

static VALUE
rb_ary_drop(VALUE ary, VALUE n)
{
    VALUE result;
    long pos = NUM2LONG(n);
    if (pos < 0) {
	rb_raise(rb_eArgError, "attempt to drop negative size");
    }

    result = rb_ary_subseq(ary, pos, RARRAY_LEN(ary));
    if (result == Qnil) result = rb_ary_new();
    return result;
}

/*
 *  call-seq:
 *     ary.drop_while { |arr| block }   -> new_ary
 *     ary.drop_while                  -> Enumerator
 *
 *  Drops elements up to, but not including, the first element for which the
 *  block returns +nil+ or +false+ and returns an array containing the
 *  remaining elements.
 *
 *  If no block is given, an Enumerator is returned instead.
 *
 *  See also Array#take_while
 *
 *     a = [1, 2, 3, 4, 5, 0]
 *     a.drop_while {|i| i < 3 }   #=> [3, 4, 5, 0]
 *
 */

static VALUE
rb_ary_drop_while(VALUE ary)
{
    long i;

    RETURN_ENUMERATOR(ary, 0, 0);
    for (i = 0; i < RARRAY_LEN(ary); i++) {
	if (!RTEST(rb_yield(RARRAY_PTR(ary)[i]))) break;
    }
    return rb_ary_drop(ary, LONG2FIX(i));
}

/*
 *  Arrays are ordered, integer-indexed collections of any object.
 *
 *  Array indexing starts at 0, as in C or Java.  A negative index is assumed
 *  to be relative to the end of the array---that is, an index of -1 indicates
 *  the last element of the array, -2 is the next to last element in the
 *  array, and so on.
 *
 *  == Creating Arrays
 *
 *  A new array can be created by using the literal constructor
 *  <code>[]</code>.  Arrays can contain different types of objects.  For
 *  example, the array below contains an Integer, a String and a Float:
 *
 *     ary = [1, "two", 3.0] #=> [1, "two", 3.0]
 *
 *  An array can also be created by explicitly calling Array.new with zero, one
 *  (the initial size of the Array) or two arguments (the initial size and a
 *  default object).
 *
 *     ary = Array.new    #=> []
 *     Array.new(3)       #=> [nil, nil, nil]
 *     Array.new(3, true) #=> [0, 0, 0]
 *
 *  Note that the second argument populates the array with references the same
 *  object.  Therefore, it is only recommended in cases when you need to
 *  instantiate arrays with natively immutable objects such Symbols, numbers,
 *  true or false.
 *
 *  To create an array with separate objects a block can be passed instead.
 *  This method is safe to use with mutable objects such as hashes, strings or
 *  other arrays:
 *
 *     Array.new(4) { Hash.new } #=> [{}, {}, {}, {}]
 *
 *  This is also a quick way to build up multi-dimensional arrays:
 *
 *     empty_table = Array.new(3) { Array.new(3) }
 *     #=> [[nil, nil, nil], [nil, nil, nil], [nil, nil, nil]]
 *
 *  == Example Usage
 *
 *  In addition to the methods it mixes in through the Enumerable module, the
 *  Array class has proprietary methods for accessing, searching and otherwise
 *  manipulating arrays.
 *
 *  Some of the more common ones are illustrated below.
 *
 *  == Accessing Elements
 *
 *  Elements in an array can be retrieved using the Array#[] method.  It can
 *  take a single integer argument (a numeric index), a pair of arguments
 *  (start and length) or a range.
 *
 *     arr = [1, 2, 3, 4, 5, 6]
 *     arr[2]    #=> 3
 *     arr[100]  #=> nil
 *     arr[-3]   #=> 4
 *     arr[2, 3] #=> [3, 4, 5]
 *     arr[1..4] #=> [2, 3, 4, 5]
 *
 *  Another way to access a particular array element is by using the #at method
 *
 *     arr.at(0) #=> 1
 *
 *  The #slice method works in an identical manner to Array#[].
 *
 *  To raise an error for indices outside of the array bounds or else to
 *  provide a default value when that happens, you can use #fetch.
 *
 *     arr = ['a', 'b', 'c', 'd', 'e', 'f']
 *     arr.fetch(100) #=> IndexError: index 100 outside of array bounds: -6...6
 *     arr.fetch(100, "oops") #=> "oops"
 *
 *  The special methods #first and #last will return the first and last
 *  elements of an array, respectively.
 *
 *     arr.first #=> 1
 *     arr.last  #=> 6
 *
 *  To return the first +n+ elements of an array, use #take
 *
 *     arr.take(3) #=> [1, 2, 3]
 *
 *  #drop does the opposite of #take, by returning the elements after +n+
 *  elements have been dropped:
 *
 *     arr.drop(3) #=> [4, 5, 6]
 *
 *  == Obtaining Information about an Array
 *
 *  Arrays keep track of their own length at all times.  To query an array
 *  about the number of elements it contains, use #length, #count or #size.
 *
 *    browsers = ['Chrome', 'Firefox', 'Safari', 'Opera', 'IE']
 *    browsers.length #=> 5
 *    browsers.count #=> 5
 *
 *  To check whether an array contains any elements at all
 *
 *    browsers.empty? #=> false
 *
 *  To check whether a particular item is included in the array
 *
 *    browsers.include?('Konqueror') #=> false
 *
 *  == Adding Items to Arrays
 *
 *  Items can be added to the end of an array by using either #push or #<<
 *
 *    arr = [1, 2, 3, 4]
 *    arr.push(5) #=> [1, 2, 3, 4, 5]
 *    arr << 6    #=> [1, 2, 3, 4, 5, 6]
 *
 *  #unshift will add a new item to the beginning of an array.
 *
 *     arr.unshift(0) #=> [0, 1, 2, 3, 4, 5, 6]
 *
 *  With #insert you can add a new element to an array at any position.
 *
 *     arr.insert(3, 'apple')  #=> [0, 1, 2, 'apple', 3, 4, 5, 6]
 *
 *  Using the #insert method, you can also insert multiple values at once:
 *
 *     arr.insert(3, 'orange', 'pear', 'grapefruit')
 *     #=> [0, 1, 2, "orange", "pear", "grapefruit", "apple", 3, 4, 5, 6]
 *
 *  == Removing Items from an Array
 *
 *  The method #pop removes the last element in an array and returns it:
 *
 *     arr =  [1, 2, 3, 4, 5, 6]
 *     arr.pop #=> 6
 *     arr #=> [1, 2, 3, 4, 5]
 *
 *  To retrieve and at the same time remove the first item, use #shift:
 *
 *     arr.shift #=> 1
 *     arr #=> [2, 3, 4, 5]
 *
 *  To delete an element at a particular index:
 *
 *     arr.delete_at(2) #=> 4
 *     arr #=> [2, 3, 5]
 *
 *  To delete a particular element anywhere in an array, use #delete:
 *
 *     arr = [1, 2, 2, 3]
 *     arr.delete(2) #=> [1, 3]
 *
 *  A useful method if you need to remove +nil+ values from an array is
 *  #compact:
 *
 *     arr = ['foo', 0, nil, 'bar', 7, 'baz', nil]
 *     arr.compact  #=> ['foo', 0, 'bar', 7, 'baz']
 *     arr          #=> ['foo', 0, nil, 'bar', 7, 'baz', nil]
 *     arr.compact! #=> ['foo', 0, 'bar', 7, 'baz']
 *     arr          #=> ['foo', 0, 'bar', 7, 'baz']
 *
 *  Another common need is to remove duplicate elements from an array.
 *
 *  It has the non-destructive #uniq, and destructive method #uniq!
 *
 *     arr = [2, 5, 6, 556, 6, 6, 8, 9, 0, 123, 556]
 *     arr.uniq #=> [2, 5, 6, 556, 8, 9, 0, 123]
 *
 *  == Iterating over Arrays
 *
 *  Like all classes that include the Enumerable module, Array has an each
 *  method, which defines what elements should be iterated over and how.  In
 *  case of Array's #each, all elements in the Array instance are yielded to
 *  the supplied block in sequence.
 *
 *  Note that this operation leaves the array unchanged.
 *
 *     arr = [1, 2, 3, 4, 5]
 *     arr.each { |a| print a -= 10, " " }
 *     # prints: -9 -8 -7 -6 -5
 *     #=> [1, 2, 3, 4, 5]
 *
 *  Another sometimes useful iterator is #reverse_each which will iterate over
 *  the elements in the array in reverse order.
 *
 *     words = %w[rats live on no evil star]
 *     str = ""
 *     words.reverse_each { |word| str += "#{word.reverse} " }
 *     str #=> "rats live on no evil star "
 *
 *  The #map method can be used to create a new array based on the original
 *  array, but with the values modified by the supplied block:
 *
 *     arr.map { |a| 2*a }   #=> [2, 4, 6, 8, 10]
 *     arr                   #=> [1, 2, 3, 4, 5]
 *     arr.map! { |a| a**2 } #=> [1, 4, 9, 16, 25]
 *     arr                   #=> [1, 4, 9, 16, 25]
 *
 *  == Selecting Items from an Array
 *
 *  Elements can be selected from an array according to criteria defined in a
 *  block.  The selection can happen in a destructive or a non-destructive
 *  manner.  While the destructive operations will modify the array they were
 *  called on, the non-destructive methods usually return a new array with the
 *  selected elements, but leave the original array unchanged.
 *
 *  === Non-destructive Selection
 *
 *     arr = [1, 2, 3, 4, 5, 6]
 *     arr.select { |a| a > 3 }     #=> [4, 5, 6]
 *     arr.reject { |a| a < 3 }     #=> [4, 5, 6]
 *     arr.drop_while { |a| a < 4 } #=> [4, 5, 6]
 *     arr                          #=> [1, 2, 3, 4, 5, 6]
 *
 *  === Destructive Selection
 *
 *  #select! and #reject! are the corresponding destructive methods to #select
 *  and #reject
 *
 *  Similar to #select vs. #reject, #delete_if and #keep_if have the exact
 *  opposite result when supplied with the same block:
 *
 *     arr.delete_if { |a| a < 4 } #=> [4, 5, 6]
 *     arr                         #=> [4, 5, 6]
 *
 *     arr = [1, 2, 3, 4, 5, 6]
 *     arr.keep_if { |a| a < 4 } #=> [1, 2, 3]
 *     arr                       #=> [1, 2, 3]
 *
 */

void
Init_Array(void)
{
#undef rb_intern
#define rb_intern(str) rb_intern_const(str)

    rb_cArray  = rb_define_class("Array", rb_cObject);
    rb_include_module(rb_cArray, rb_mEnumerable);

    rb_define_alloc_func(rb_cArray, ary_alloc);
    rb_define_singleton_method(rb_cArray, "[]", rb_ary_s_create, -1);
    rb_define_singleton_method(rb_cArray, "try_convert", rb_ary_s_try_convert, 1);
    rb_define_method(rb_cArray, "initialize", rb_ary_initialize, -1);
    rb_define_method(rb_cArray, "initialize_copy", rb_ary_replace, 1);

    rb_define_method(rb_cArray, "inspect", rb_ary_inspect, 0);
    rb_define_alias(rb_cArray,  "to_s", "inspect");
    rb_define_method(rb_cArray, "to_a", rb_ary_to_a, 0);
    rb_define_method(rb_cArray, "to_ary", rb_ary_to_ary_m, 0);
    rb_define_method(rb_cArray, "frozen?",  rb_ary_frozen_p, 0);

    rb_define_method(rb_cArray, "==", rb_ary_equal, 1);
    rb_define_method(rb_cArray, "eql?", rb_ary_eql, 1);
    rb_define_method(rb_cArray, "hash", rb_ary_hash, 0);

    rb_define_method(rb_cArray, "[]", rb_ary_aref, -1);
    rb_define_method(rb_cArray, "[]=", rb_ary_aset, -1);
    rb_define_method(rb_cArray, "at", rb_ary_at, 1);
    rb_define_method(rb_cArray, "fetch", rb_ary_fetch, -1);
    rb_define_method(rb_cArray, "first", rb_ary_first, -1);
    rb_define_method(rb_cArray, "last", rb_ary_last, -1);
    rb_define_method(rb_cArray, "concat", rb_ary_concat, 1);
    rb_define_method(rb_cArray, "<<", rb_ary_push, 1);
    rb_define_method(rb_cArray, "push", rb_ary_push_m, -1);
    rb_define_method(rb_cArray, "pop", rb_ary_pop_m, -1);
    rb_define_method(rb_cArray, "shift", rb_ary_shift_m, -1);
    rb_define_method(rb_cArray, "unshift", rb_ary_unshift_m, -1);
    rb_define_method(rb_cArray, "insert", rb_ary_insert, -1);
    rb_define_method(rb_cArray, "each", rb_ary_each, 0);
    rb_define_method(rb_cArray, "each_index", rb_ary_each_index, 0);
    rb_define_method(rb_cArray, "reverse_each", rb_ary_reverse_each, 0);
    rb_define_method(rb_cArray, "length", rb_ary_length, 0);
    rb_define_alias(rb_cArray,  "size", "length");
    rb_define_method(rb_cArray, "empty?", rb_ary_empty_p, 0);
    rb_define_method(rb_cArray, "find_index", rb_ary_index, -1);
    rb_define_method(rb_cArray, "index", rb_ary_index, -1);
    rb_define_method(rb_cArray, "rindex", rb_ary_rindex, -1);
    rb_define_method(rb_cArray, "join", rb_ary_join_m, -1);
    rb_define_method(rb_cArray, "reverse", rb_ary_reverse_m, 0);
    rb_define_method(rb_cArray, "reverse!", rb_ary_reverse_bang, 0);
    rb_define_method(rb_cArray, "rotate", rb_ary_rotate_m, -1);
    rb_define_method(rb_cArray, "rotate!", rb_ary_rotate_bang, -1);
    rb_define_method(rb_cArray, "sort", rb_ary_sort, 0);
    rb_define_method(rb_cArray, "sort!", rb_ary_sort_bang, 0);
    rb_define_method(rb_cArray, "sort_by!", rb_ary_sort_by_bang, 0);
    rb_define_method(rb_cArray, "collect", rb_ary_collect, 0);
    rb_define_method(rb_cArray, "collect!", rb_ary_collect_bang, 0);
    rb_define_method(rb_cArray, "map", rb_ary_collect, 0);
    rb_define_method(rb_cArray, "map!", rb_ary_collect_bang, 0);
    rb_define_method(rb_cArray, "select", rb_ary_select, 0);
    rb_define_method(rb_cArray, "select!", rb_ary_select_bang, 0);
    rb_define_method(rb_cArray, "keep_if", rb_ary_keep_if, 0);
    rb_define_method(rb_cArray, "values_at", rb_ary_values_at, -1);
    rb_define_method(rb_cArray, "delete", rb_ary_delete, 1);
    rb_define_method(rb_cArray, "delete_at", rb_ary_delete_at_m, 1);
    rb_define_method(rb_cArray, "delete_if", rb_ary_delete_if, 0);
    rb_define_method(rb_cArray, "reject", rb_ary_reject, 0);
    rb_define_method(rb_cArray, "reject!", rb_ary_reject_bang, 0);
    rb_define_method(rb_cArray, "zip", rb_ary_zip, -1);
    rb_define_method(rb_cArray, "transpose", rb_ary_transpose, 0);
    rb_define_method(rb_cArray, "replace", rb_ary_replace, 1);
    rb_define_method(rb_cArray, "clear", rb_ary_clear, 0);
    rb_define_method(rb_cArray, "fill", rb_ary_fill, -1);
    rb_define_method(rb_cArray, "include?", rb_ary_includes, 1);
    rb_define_method(rb_cArray, "<=>", rb_ary_cmp, 1);

    rb_define_method(rb_cArray, "slice", rb_ary_aref, -1);
    rb_define_method(rb_cArray, "slice!", rb_ary_slice_bang, -1);

    rb_define_method(rb_cArray, "assoc", rb_ary_assoc, 1);
    rb_define_method(rb_cArray, "rassoc", rb_ary_rassoc, 1);

    rb_define_method(rb_cArray, "+", rb_ary_plus, 1);
    rb_define_method(rb_cArray, "*", rb_ary_times, 1);

    rb_define_method(rb_cArray, "-", rb_ary_diff, 1);
    rb_define_method(rb_cArray, "&", rb_ary_and, 1);
    rb_define_method(rb_cArray, "|", rb_ary_or, 1);

    rb_define_method(rb_cArray, "uniq", rb_ary_uniq, 0);
    rb_define_method(rb_cArray, "uniq!", rb_ary_uniq_bang, 0);
    rb_define_method(rb_cArray, "compact", rb_ary_compact, 0);
    rb_define_method(rb_cArray, "compact!", rb_ary_compact_bang, 0);
    rb_define_method(rb_cArray, "flatten", rb_ary_flatten, -1);
    rb_define_method(rb_cArray, "flatten!", rb_ary_flatten_bang, -1);
    rb_define_method(rb_cArray, "count", rb_ary_count, -1);
    rb_define_method(rb_cArray, "shuffle!", rb_ary_shuffle_bang, -1);
    rb_define_method(rb_cArray, "shuffle", rb_ary_shuffle, -1);
    rb_define_method(rb_cArray, "sample", rb_ary_sample, -1);
    rb_define_method(rb_cArray, "cycle", rb_ary_cycle, -1);
    rb_define_method(rb_cArray, "permutation", rb_ary_permutation, -1);
    rb_define_method(rb_cArray, "combination", rb_ary_combination, 1);
    rb_define_method(rb_cArray, "repeated_permutation", rb_ary_repeated_permutation, 1);
    rb_define_method(rb_cArray, "repeated_combination", rb_ary_repeated_combination, 1);
    rb_define_method(rb_cArray, "product", rb_ary_product, -1);

    rb_define_method(rb_cArray, "take", rb_ary_take, 1);
    rb_define_method(rb_cArray, "take_while", rb_ary_take_while, 0);
    rb_define_method(rb_cArray, "drop", rb_ary_drop, 1);
    rb_define_method(rb_cArray, "drop_while", rb_ary_drop_while, 0);

    id_cmp = rb_intern("<=>");
    sym_random = ID2SYM(rb_intern("random"));
}