116 lines
3.2 KiB
C
116 lines
3.2 KiB
C
/* mpz_clrbit -- clear a specified bit.
|
|
|
|
Copyright 1991, 1993, 1994, 1995, 2001, 2002 Free Software Foundation, Inc.
|
|
|
|
This file is part of the GNU MP Library.
|
|
|
|
The GNU MP Library is free software; you can redistribute it and/or modify
|
|
it under the terms of the GNU Lesser General Public License as published by
|
|
the Free Software Foundation; either version 2.1 of the License, or (at your
|
|
option) any later version.
|
|
|
|
The GNU MP Library 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 Lesser General Public
|
|
License for more details.
|
|
|
|
You should have received a copy of the GNU Lesser General Public License
|
|
along with the GNU MP Library; see the file COPYING.LIB. If not, write to
|
|
the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
|
|
MA 02110-1301, USA. */
|
|
|
|
#include "mpir.h"
|
|
#include "gmp-impl.h"
|
|
|
|
void
|
|
mpz_clrbit (mpz_ptr d, mp_bitcnt_t bit_index)
|
|
{
|
|
mp_size_t dsize = d->_mp_size;
|
|
mp_ptr dp = d->_mp_d;
|
|
mp_size_t limb_index;
|
|
|
|
limb_index = bit_index / GMP_NUMB_BITS;
|
|
if (dsize >= 0)
|
|
{
|
|
if (limb_index < dsize)
|
|
{
|
|
mp_limb_t dlimb;
|
|
dlimb = dp[limb_index];
|
|
dlimb &= ~((mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS));
|
|
dp[limb_index] = dlimb;
|
|
|
|
if (UNLIKELY (dlimb == 0 && limb_index == dsize-1))
|
|
{
|
|
/* high limb became zero, must normalize */
|
|
do {
|
|
dsize--;
|
|
} while (dsize > 0 && dp[dsize-1] == 0);
|
|
d->_mp_size = dsize;
|
|
}
|
|
}
|
|
else
|
|
;
|
|
}
|
|
else
|
|
{
|
|
mp_size_t zero_bound;
|
|
|
|
/* Simulate two's complement arithmetic, i.e. simulate
|
|
1. Set OP = ~(OP - 1) [with infinitely many leading ones].
|
|
2. clear the bit.
|
|
3. Set OP = ~OP + 1. */
|
|
|
|
dsize = -dsize;
|
|
|
|
/* No upper bound on this loop, we're sure there's a non-zero limb
|
|
sooner ot later. */
|
|
for (zero_bound = 0; ; zero_bound++)
|
|
if (dp[zero_bound] != 0)
|
|
break;
|
|
|
|
if (limb_index > zero_bound)
|
|
{
|
|
if (limb_index < dsize)
|
|
dp[limb_index] |= (mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS);
|
|
else
|
|
{
|
|
/* Ugh. The bit should be cleared outside of the end of the
|
|
number. We have to increase the size of the number. */
|
|
if (UNLIKELY (d->_mp_alloc < limb_index + 1))
|
|
dp = _mpz_realloc (d, limb_index + 1);
|
|
|
|
MPN_ZERO (dp + dsize, limb_index - dsize);
|
|
dp[limb_index] = (mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS);
|
|
d->_mp_size = -(limb_index + 1);
|
|
}
|
|
}
|
|
else if (limb_index == zero_bound)
|
|
{
|
|
dp[limb_index] = ((((dp[limb_index] - 1)
|
|
| ((mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS))) + 1)
|
|
& GMP_NUMB_MASK);
|
|
if (dp[limb_index] == 0)
|
|
{
|
|
mp_size_t i;
|
|
for (i = limb_index + 1; i < dsize; i++)
|
|
{
|
|
dp[i] = (dp[i] + 1) & GMP_NUMB_MASK;
|
|
if (dp[i] != 0)
|
|
goto fin;
|
|
}
|
|
/* We got carry all way out beyond the end of D. Increase
|
|
its size (and allocation if necessary). */
|
|
dsize++;
|
|
if (UNLIKELY (d->_mp_alloc < dsize))
|
|
dp = _mpz_realloc (d, dsize);
|
|
|
|
dp[i] = 1;
|
|
d->_mp_size = -dsize;
|
|
fin:;
|
|
}
|
|
}
|
|
else
|
|
;
|
|
}
|
|
}
|