min_heap.h

/*
 * Copyright (c) 2006 Maxim Yegorushkin <maxim.yegorushkin@gmail.com>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
#ifndef _MIN_HEAP_H_
#define _MIN_HEAP_H_

#include "event2/event.h"

typedef struct min_heap
{
    struct event** p;
    unsigned n, a;
} min_heap_t;

static inline void           min_heap_ctor(min_heap_t* s);
static inline void           min_heap_dtor(min_heap_t* s);
static inline void           min_heap_elem_init(struct event* e);
static inline int            min_heap_elem_greater(struct event *a, struct event *b);
static inline int            min_heap_empty(min_heap_t* s);
static inline unsigned       min_heap_size(min_heap_t* s);
static inline struct event*  min_heap_top(min_heap_t* s);
static inline int            min_heap_reserve(min_heap_t* s, unsigned n);
static inline int            min_heap_push(min_heap_t* s, struct event* e);
static inline struct event*  min_heap_pop(min_heap_t* s);
static inline int            min_heap_erase(min_heap_t* s, struct event* e);
static inline void           min_heap_shift_up_(min_heap_t* s, unsigned hole_index, struct event* e);
static inline void           min_heap_shift_down_(min_heap_t* s, unsigned hole_index, struct event* e);

int min_heap_elem_greater(struct event *a, struct event *b)
{
    return timercmp(&a->ev_timeout, &b->ev_timeout, >);
}

void min_heap_ctor(min_heap_t* s) { s->p = 0; s->n = 0; s->a = 0; }
void min_heap_dtor(min_heap_t* s) { free(s->p); }
void min_heap_elem_init(struct event* e) { e->min_heap_idx = -1; }
int min_heap_empty(min_heap_t* s) { return 0u == s->n; }
unsigned min_heap_size(min_heap_t* s) { return s->n; }
struct event* min_heap_top(min_heap_t* s) { return s->n ? *s->p : 0; }

int min_heap_push(min_heap_t* s, struct event* e)
{
    if(min_heap_reserve(s, s->n + 1))
        return -1;
    min_heap_shift_up_(s, s->n++, e);
    return 0;
}

struct event* min_heap_pop(min_heap_t* s)
{
    if(s->n)
    {
        struct event* e = *s->p;
        e->min_heap_idx = -1;
        min_heap_shift_down_(s, 0u, s->p[--s->n]);
        return e;
    }
    return 0;
}

int min_heap_erase(min_heap_t* s, struct event* e)
{
    if(((unsigned int)-1) != e->min_heap_idx)
    {
        min_heap_shift_down_(s, e->min_heap_idx, s->p[--s->n]);
        e->min_heap_idx = -1;
        return 0;
    }
    return -1;
}

int min_heap_reserve(min_heap_t* s, unsigned n)
{
    if(s->a < n)
    {
        struct event** p;
        unsigned a = s->a ? s->a * 2 : 8;
        if(a < n)
            a = n;
        if(!(p = (struct event**)realloc(s->p, a * sizeof *p)))
            return -1;
        s->p = p;
        s->a = a;
    }
    return 0;
}

void min_heap_shift_up_(min_heap_t* s, unsigned hole_index, struct event* e)
{
    unsigned parent = (hole_index - 1) / 2;
    while(hole_index && min_heap_elem_greater(s->p[parent], e))
    {
        (s->p[hole_index] = s->p[parent])->min_heap_idx = hole_index;
        hole_index = parent;
        parent = (hole_index - 1) / 2;
    }
    (s->p[hole_index] = e)->min_heap_idx = hole_index;
}

void min_heap_shift_down_(min_heap_t* s, unsigned hole_index, struct event* e)
{
    unsigned min_child = 2 * (hole_index + 1);
    while(min_child <= s->n)
	{
        min_child -= min_child == s->n || min_heap_elem_greater(s->p[min_child], s->p[min_child - 1]);
        if(!(min_heap_elem_greater(e, s->p[min_child])))
            break;
        (s->p[hole_index] = s->p[min_child])->min_heap_idx = hole_index;
        hole_index = min_child;
        min_child = 2 * (hole_index + 1);
	}
    min_heap_shift_up_(s, hole_index,  e);
}

#endif /* _MIN_HEAP_H_ */