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bit_unpack.c
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/*=============================================================================
This file is part of FLINT.
FLINT is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
FLINT is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with FLINT; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
=============================================================================*/
/******************************************************************************
Copyright (C) 2010 William Hart
******************************************************************************/
#include <gmp.h>
#include "flint.h"
#include "fmpz.h"
int
fmpz_bit_unpack(fmpz_t coeff, mp_srcptr arr, mp_bitcnt_t shift,
mp_bitcnt_t bits, int negate, int borrow)
{
mp_limb_t mask, sign;
ulong limbs = (shift + bits) / FLINT_BITS;
ulong rem_bits = (shift + bits) % FLINT_BITS;
/* determine if field is positive or negative */
if (rem_bits)
sign = ((((mp_limb_t) 1) << (rem_bits - 1)) & arr[limbs]);
else
sign = ((((mp_limb_t) 1) << (FLINT_BITS - 1)) & arr[limbs - 1]);
if (bits <= FLINT_BITS - 2) /* fits into a small coeff */
{
_fmpz_demote(coeff);
/* mask for the given number of bits */
mask = (((mp_limb_t) 1) << bits) - (mp_limb_t) 1;
if (limbs + (rem_bits != 0) > 1) /* field crosses a limb boundary */
(*coeff) =
((arr[0] >> shift) + (arr[1] << (FLINT_BITS - shift))) & mask;
else /* field is in first limb only, mask it */
(*coeff) = (arr[0] >> shift) & mask;
/* sign extend */
if (sign)
(*coeff) += ((~(mp_limb_t) 0) << bits);
/* determine whether we need to return a borrow */
sign = (*coeff < (mp_limb_signed_t) 0 ? (mp_limb_t) 1 : (mp_limb_t) 0);
/* deal with borrow */
if (borrow)
{
(*coeff)++;
if ((*coeff) > COEFF_MAX)
{
fmpz v = *coeff;
*coeff = 0;
fmpz_set_ui(coeff, v);
}
}
/* negate the coeff if necessary */
if (negate)
fmpz_neg(coeff, coeff);
return (sign != (mp_limb_t) 0);
}
else /* large coefficient */
{
__mpz_struct * mpz_ptr;
mp_limb_t * p;
ulong l, b;
mpz_ptr = _fmpz_promote(coeff);
/* the number of limbs to hold the bitfield _including_ b extra bits */
l = (bits - 1) / FLINT_BITS + 1;
b = bits % FLINT_BITS;
/* allocate space for l limbs only */
mpz_realloc(mpz_ptr, l);
p = mpz_ptr->_mp_d;
/* shift in l limbs */
if (shift)
mpn_rshift(p, arr, l, shift);
else
flint_mpn_copyi(p, arr, l);
/* shift in any rem_bits that weren't already shifted */
if (limbs + (rem_bits != 0) > l)
p[l - 1] += (arr[limbs] << (FLINT_BITS - shift));
/* mask off the last limb, if not full */
if (b)
{
mask = (((mp_limb_t) 1) << b) - (mp_limb_t) 1;
p[l - 1] &= mask;
}
if (sign != (mp_limb_t) 0)
{
/* sign extend */
if (b)
p[l - 1] += ((~(mp_limb_t) 0) << b);
/* negate */
mpn_com_n(p, p, l);
if (!borrow)
mpn_add_1(p, p, l, 1);
/* normalise */
while (l && (p[l - 1] == (mp_limb_t) 0))
l--;
mpz_ptr->_mp_size = -l;
sign = 1;
}
else
{
/* deal with borrow */
if (borrow)
mpn_add_1(p, p, l, 1);
/* normalise */
while (l && (p[l - 1] == (mp_limb_t) 0))
l--;
mpz_ptr->_mp_size = l;
sign = 0;
}
/* negate if required */
if (negate)
mpz_neg(mpz_ptr, mpz_ptr);
/* coeff may fit in a small */
_fmpz_demote_val(coeff);
return sign;
}
}
void
fmpz_bit_unpack_unsigned(fmpz_t coeff, mp_srcptr arr,
mp_bitcnt_t shift, mp_bitcnt_t bits)
{
ulong limbs = (shift + bits) / FLINT_BITS;
ulong rem_bits = (shift + bits) % FLINT_BITS;
mp_limb_t mask;
if (bits <= FLINT_BITS - 2) /* fits into a small coeff */
{
_fmpz_demote(coeff);
/* mask for the given number of bits */
mask = (((mp_limb_t) 1) << bits) - (mp_limb_t) 1;
if (limbs + (rem_bits != 0) > 1) /* field crosses a limb boundary */
(*coeff) =
((arr[0] >> shift) + (arr[1] << (FLINT_BITS - shift))) & mask;
else /* field is in first limb only, mask it */
(*coeff) = (arr[0] >> shift) & mask;
}
else /* large coefficient */
{
__mpz_struct * mpz_ptr;
mp_limb_t * p;
ulong l, b;
mpz_ptr = _fmpz_promote(coeff);
/* the number of limbs to hold the bitfield _including_ b extra bits */
l = (bits - 1) / FLINT_BITS + 1;
b = bits % FLINT_BITS;
/* allocate space for l limbs only */
mpz_realloc(mpz_ptr, l);
p = mpz_ptr->_mp_d;
/* shift in l limbs */
if (shift)
mpn_rshift(p, arr, l, shift);
else
flint_mpn_copyi(p, arr, l);
/* shift in any rem_bits that weren't already shifted */
if (limbs + (rem_bits != 0) > l)
p[l - 1] += (arr[limbs] << (FLINT_BITS - shift));
/* mask off the last limb, if not full */
if (b)
{
mask = (((mp_limb_t) 1) << b) - (mp_limb_t) 1;
p[l - 1] &= mask;
}
/* normalise */
while (l && (p[l - 1] == (mp_limb_t) 0))
l--;
mpz_ptr->_mp_size = l;
/* coeff may fit in a small */
_fmpz_demote_val(coeff);
}
}