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/* mpz_combit -- complement a specified bit.
Copyright 2002, 2003, 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_combit (mpz_ptr d, mp_bitcnt_t bit_index)
{
mp_size_t dsize = SIZ(d);
mp_ptr dp = PTR(d);
mp_size_t limb_index = bit_index / GMP_NUMB_BITS;
mp_limb_t bit = (CNST_LIMB (1) << (bit_index % GMP_NUMB_BITS));
/* Check for the most common case: Positive input, no realloc or
normalization needed. */
if (limb_index + 1 < dsize)
dp[limb_index] ^= bit;
/* Check for the hairy case. d < 0, and we have all zero bits to the
right of the bit to toggle. */
else if (limb_index < -dsize && mpn_zero_p (dp, limb_index)
&& (dp[limb_index] & (bit - 1)) == 0)
{
ASSERT (dsize < 0);
dsize = -dsize;
if (dp[limb_index] & bit)
{
/* We toggle the least significant one bit. Corresponds to
an add, with potential carry propagation, on the absolute
value. */
dp = MPZ_REALLOC (d, 1 + dsize);
dp[dsize] = 0;
MPN_INCR_U (dp + limb_index, 1 + dsize - limb_index, bit);
SIZ(d) -= dp[dsize];
}
else
{
/* We toggle a zero bit, subtract from the absolute value. */
MPN_DECR_U (dp + limb_index, dsize - limb_index, bit);
MPN_NORMALIZE (dp, dsize);
ASSERT (dsize > 0);
SIZ(d) = -dsize;
}
}
else
{
/* Simple case: Toggle the bit in the absolute value. */
dsize = ABS(dsize);
if (limb_index < dsize)
{
dp[limb_index] ^= bit;
/* Can happen only when limb_index = dsize - 1. Avoid SIZ(d)
bookkeeping in the common case. */
if (dp[dsize-1] == 0)
{
dsize--;
MPN_NORMALIZE (dp, dsize);
SIZ (d) = SIZ (d) >= 0 ? dsize : -dsize;
}
}
else
{
dp = MPZ_REALLOC (d, limb_index + 1);
MPN_ZERO(dp + dsize, limb_index - dsize);
dp[limb_index++] = bit;
SIZ(d) = SIZ(d) >= 0 ? limb_index : -limb_index;
}
}
}
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