186d7f5d3SJohn Marino /* mpz_combit -- complement a specified bit.
286d7f5d3SJohn Marino
386d7f5d3SJohn Marino Copyright 2002, 2003 Free Software Foundation, Inc.
486d7f5d3SJohn Marino
586d7f5d3SJohn Marino This file is part of the GNU MP Library.
686d7f5d3SJohn Marino
786d7f5d3SJohn Marino The GNU MP Library is free software; you can redistribute it and/or modify
886d7f5d3SJohn Marino it under the terms of the GNU Lesser General Public License as published by
986d7f5d3SJohn Marino the Free Software Foundation; either version 3 of the License, or (at your
1086d7f5d3SJohn Marino option) any later version.
1186d7f5d3SJohn Marino
1286d7f5d3SJohn Marino The GNU MP Library is distributed in the hope that it will be useful, but
1386d7f5d3SJohn Marino WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
1486d7f5d3SJohn Marino or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
1586d7f5d3SJohn Marino License for more details.
1686d7f5d3SJohn Marino
1786d7f5d3SJohn Marino You should have received a copy of the GNU Lesser General Public License
1886d7f5d3SJohn Marino along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
1986d7f5d3SJohn Marino
2086d7f5d3SJohn Marino #include "gmp.h"
2186d7f5d3SJohn Marino #include "gmp-impl.h"
2286d7f5d3SJohn Marino
2386d7f5d3SJohn Marino void
mpz_combit(mpz_ptr d,mp_bitcnt_t bit_index)2486d7f5d3SJohn Marino mpz_combit (mpz_ptr d, mp_bitcnt_t bit_index)
2586d7f5d3SJohn Marino {
2686d7f5d3SJohn Marino mp_size_t dsize = ABSIZ(d);
2786d7f5d3SJohn Marino mp_ptr dp = LIMBS(d);
2886d7f5d3SJohn Marino
2986d7f5d3SJohn Marino mp_size_t limb_index = bit_index / GMP_NUMB_BITS;
3086d7f5d3SJohn Marino mp_limb_t bit = ((mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS));
3186d7f5d3SJohn Marino
3286d7f5d3SJohn Marino if (limb_index >= dsize)
3386d7f5d3SJohn Marino {
3486d7f5d3SJohn Marino MPZ_REALLOC(d, limb_index + 1);
3586d7f5d3SJohn Marino dp = LIMBS(d);
3686d7f5d3SJohn Marino
3786d7f5d3SJohn Marino MPN_ZERO(dp + dsize, limb_index + 1 - dsize);
3886d7f5d3SJohn Marino dsize = limb_index + 1;
3986d7f5d3SJohn Marino }
4086d7f5d3SJohn Marino
4186d7f5d3SJohn Marino if (SIZ(d) >= 0)
4286d7f5d3SJohn Marino {
4386d7f5d3SJohn Marino dp[limb_index] ^= bit;
4486d7f5d3SJohn Marino MPN_NORMALIZE (dp, dsize);
4586d7f5d3SJohn Marino SIZ(d) = dsize;
4686d7f5d3SJohn Marino }
4786d7f5d3SJohn Marino else
4886d7f5d3SJohn Marino {
4986d7f5d3SJohn Marino mp_limb_t x = -dp[limb_index];
5086d7f5d3SJohn Marino mp_size_t i;
5186d7f5d3SJohn Marino
5286d7f5d3SJohn Marino /* non-zero limb below us means ones-complement */
5386d7f5d3SJohn Marino for (i = limb_index-1; i >= 0; i--)
5486d7f5d3SJohn Marino if (dp[i] != 0)
5586d7f5d3SJohn Marino {
5686d7f5d3SJohn Marino x--; /* change twos comp to ones comp */
5786d7f5d3SJohn Marino break;
5886d7f5d3SJohn Marino }
5986d7f5d3SJohn Marino
6086d7f5d3SJohn Marino if (x & bit)
6186d7f5d3SJohn Marino {
6286d7f5d3SJohn Marino mp_limb_t c;
6386d7f5d3SJohn Marino
6486d7f5d3SJohn Marino /* Clearing the bit increases the magitude. We might need a carry. */
6586d7f5d3SJohn Marino MPZ_REALLOC(d, dsize + 1);
6686d7f5d3SJohn Marino dp = LIMBS(d);
6786d7f5d3SJohn Marino
6886d7f5d3SJohn Marino __GMPN_ADD_1 (c, dp+limb_index, dp+limb_index,
6986d7f5d3SJohn Marino dsize - limb_index, bit);
7086d7f5d3SJohn Marino dp[dsize] = c;
7186d7f5d3SJohn Marino dsize += c;
7286d7f5d3SJohn Marino }
7386d7f5d3SJohn Marino else
7486d7f5d3SJohn Marino /* Setting the bit decreases the magnitude */
7586d7f5d3SJohn Marino mpn_sub_1(dp+limb_index, dp+limb_index, dsize + limb_index, bit);
7686d7f5d3SJohn Marino
7786d7f5d3SJohn Marino MPN_NORMALIZE (dp, dsize);
7886d7f5d3SJohn Marino SIZ(d) = -dsize;
7986d7f5d3SJohn Marino }
8086d7f5d3SJohn Marino }
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