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/* 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 3 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. If not, see http://www.gnu.org/licenses/. */
#include "gmp.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. */
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++;
dp = MPZ_REALLOC (d, dsize);
dp[i] = 1;
d->_mp_size = -dsize;
fin:;
}
}
else
;
}
}
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