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/* mpz_clrbit -- clear a specified bit.
Copyright 1991, 1993, 1994, 1995, 2001, 2002, 2012 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_idx)
{
mp_size_t dsize = SIZ (d);
mp_ptr dp = PTR (d);
mp_size_t limb_idx;
mp_limb_t mask;
limb_idx = bit_idx / GMP_NUMB_BITS;
mask = CNST_LIMB(1) << (bit_idx % GMP_NUMB_BITS);
if (dsize >= 0)
{
if (limb_idx < dsize)
{
mp_limb_t dlimb;
dlimb = dp[limb_idx];
dlimb &= ~mask;
dp[limb_idx] = dlimb;
if (UNLIKELY (dlimb == 0 && limb_idx == dsize-1))
{
/* high limb became zero, must normalize */
MPN_NORMALIZE (dp, limb_idx);
SIZ (d) = limb_idx;
}
}
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 index upper bound on this loop, we're sure there's a non-zero limb
sooner or later. */
zero_bound = 0;
while (dp[zero_bound] == 0)
zero_bound++;
if (limb_idx > zero_bound)
{
if (limb_idx < dsize)
dp[limb_idx] |= mask;
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_idx + 1);
SIZ (d) = -(limb_idx + 1);
MPN_ZERO (dp + dsize, limb_idx - dsize);
dp[limb_idx] = mask;
}
}
else if (limb_idx == zero_bound)
{
dp[limb_idx] = ((((dp[limb_idx] - 1) | mask) + 1) & GMP_NUMB_MASK);
if (dp[limb_idx] == 0)
{
/* Increment at limb_idx + 1. Extend the number with a zero limb
for simplicity. */
dp = MPZ_REALLOC (d, dsize + 1);
dp[dsize] = 0;
MPN_INCR_U (dp + limb_idx + 1, dsize - limb_idx, 1);
dsize += dp[dsize];
SIZ (d) = -dsize;
fin:;
}
}
else
;
}
}
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