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|
/* mpz_clrbit -- clear a specified bit.
Copyright (C) 1991 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 General Public License as published by
the Free Software Foundation; either version 2, 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with the GNU MP Library; see the file COPYING. If not, write to
the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */
#include "gmp.h"
#include "gmp-impl.h"
#define MPN_NORMALIZE(p, size) \
do { \
mp_size i; \
for (i = (size) - 1; i >= 0; i--) \
if ((p)[i] != 0) \
break; \
(size) = i + 1; \
} while (0)
void
#ifdef __STDC__
mpz_clrbit (MP_INT *d, unsigned long int bit_index)
#else
mpz_clrbit (d, bit_index)
MP_INT *d;
unsigned long int bit_index;
#endif
{
mp_size dsize = d->size;
mp_ptr dp = d->d;
mp_size limb_index;
limb_index = bit_index / BITS_PER_MP_LIMB;
if (dsize >= 0)
{
if (limb_index < dsize)
{
dp[limb_index] &= ~((mp_limb) 1 << (bit_index % BITS_PER_MP_LIMB));
MPN_NORMALIZE (dp, dsize);
d->size = dsize;
}
else
;
}
else
{
mp_size 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) 1 << (bit_index % BITS_PER_MP_LIMB));
}
else
{
/* Ugh. The bit should be cleared outside of the end of the
number. We have to increase the size of the number. */
if (d->alloc < limb_index + 1)
{
_mpz_realloc (d, limb_index + 1);
dp = d->d;
}
MPN_ZERO (dp + dsize, limb_index - dsize);
dp[limb_index] = ((mp_limb) 1 << (bit_index % BITS_PER_MP_LIMB));
d->size = -(limb_index + 1);
}
}
else if (limb_index == zero_bound)
{
dp[limb_index] = ((dp[limb_index] - 1)
| ((mp_limb) 1 << (bit_index % BITS_PER_MP_LIMB))) + 1;
if (dp[limb_index] == 0)
{
mp_size i;
for (i = limb_index + 1; i < dsize; i++)
{
dp[i] += 1;
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 (d->alloc < dsize)
{
_mpz_realloc (d, dsize);
dp = d->d;
}
dp[i] = 1;
d->size = -dsize;
fin:;
}
}
else
;
}
}
|
