125 lines
3.1 KiB
C
125 lines
3.1 KiB
C
/* mpz_clrbit -- clear a specified bit.
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Copyright (C) 1991 Free Software Foundation, Inc.
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This file is part of the GNU MP Library.
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The GNU MP Library is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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The GNU MP Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with the GNU MP Library; see the file COPYING. If not, write to
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the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */
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#include "gmp.h"
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#include "gmp-impl.h"
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#define MPN_NORMALIZE(p, size) \
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do { \
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mp_size i; \
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for (i = (size) - 1; i >= 0; i--) \
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if ((p)[i] != 0) \
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break; \
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(size) = i + 1; \
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} while (0)
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void
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#ifdef __STDC__
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mpz_clrbit (MP_INT *d, unsigned long int bit_index)
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#else
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mpz_clrbit (d, bit_index)
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MP_INT *d;
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unsigned long int bit_index;
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#endif
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{
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mp_size dsize = d->size;
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mp_ptr dp = d->d;
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mp_size limb_index;
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limb_index = bit_index / BITS_PER_MP_LIMB;
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if (dsize >= 0)
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{
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if (limb_index < dsize)
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{
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dp[limb_index] &= ~((mp_limb) 1 << (bit_index % BITS_PER_MP_LIMB));
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MPN_NORMALIZE (dp, dsize);
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d->size = dsize;
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}
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else
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;
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}
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else
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{
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mp_size zero_bound;
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/* Simulate two's complement arithmetic, i.e. simulate
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1. Set OP = ~(OP - 1) [with infinitely many leading ones].
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2. clear the bit.
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3. Set OP = ~OP + 1. */
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dsize = -dsize;
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/* No upper bound on this loop, we're sure there's a non-zero limb
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sooner ot later. */
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for (zero_bound = 0; ; zero_bound++)
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if (dp[zero_bound] != 0)
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break;
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if (limb_index > zero_bound)
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{
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if (limb_index < dsize)
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{
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dp[limb_index] |= ((mp_limb) 1 << (bit_index % BITS_PER_MP_LIMB));
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}
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else
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{
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/* Ugh. The bit should be cleared outside of the end of the
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number. We have to increase the size of the number. */
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if (d->alloc < limb_index + 1)
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{
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_mpz_realloc (d, limb_index + 1);
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dp = d->d;
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}
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MPN_ZERO (dp + dsize, limb_index - dsize);
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dp[limb_index] = ((mp_limb) 1 << (bit_index % BITS_PER_MP_LIMB));
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d->size = -(limb_index + 1);
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}
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}
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else if (limb_index == zero_bound)
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{
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dp[limb_index] = ((dp[limb_index] - 1)
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| ((mp_limb) 1 << (bit_index % BITS_PER_MP_LIMB))) + 1;
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if (dp[limb_index] == 0)
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{
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mp_size i;
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for (i = limb_index + 1; i < dsize; i++)
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{
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dp[i] += 1;
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if (dp[i] != 0)
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goto fin;
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}
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/* We got carry all way out beyond the end of D. Increase
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its size (and allocation if necessary). */
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dsize++;
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if (d->alloc < dsize)
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{
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_mpz_realloc (d, dsize);
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dp = d->d;
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}
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dp[i] = 1;
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d->size = -dsize;
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fin:;
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}
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}
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else
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;
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}
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}
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