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/* mpz_combit -- complement a specified bit.
Copyright 2002, 2003 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 = ABSIZ(d);
mp_ptr dp = LIMBS(d);
mp_size_t limb_index = bit_index / GMP_NUMB_BITS;
mp_limb_t bit = ((mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS));
if (limb_index >= dsize)
{
MPZ_REALLOC(d, limb_index + 1);
dp = LIMBS(d);
MPN_ZERO(dp + dsize, limb_index + 1 - dsize);
dsize = limb_index + 1;
}
if (SIZ(d) >= 0)
{
dp[limb_index] ^= bit;
MPN_NORMALIZE (dp, dsize);
SIZ(d) = dsize;
}
else
{
mp_limb_t x = -dp[limb_index];
mp_size_t i;
/* non-zero limb below us means ones-complement */
for (i = limb_index-1; i >= 0; i--)
if (dp[i] != 0)
{
x--; /* change twos comp to ones comp */
break;
}
if (x & bit)
{
mp_limb_t c;
/* Clearing the bit increases the magitude. We might need a carry. */
MPZ_REALLOC(d, dsize + 1);
dp = LIMBS(d);
__GMPN_ADD_1 (c, dp+limb_index, dp+limb_index,
dsize - limb_index, bit);
dp[dsize] = c;
dsize += c;
}
else
/* Setting the bit decreases the magnitude */
mpn_sub_1(dp+limb_index, dp+limb_index, dsize + limb_index, bit);
MPN_NORMALIZE (dp, dsize);
SIZ(d) = -dsize;
}
}
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