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114 lines
3.1 KiB
C
114 lines
3.1 KiB
C
/* mpz_clrbit -- clear a specified bit.
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Copyright 1991, 1993, 1994, 1995, 2001, 2002 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 Lesser General Public License as published by
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the Free Software Foundation; either version 3 of the License, or (at your
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option) any later version.
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The GNU MP Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
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#include "gmp.h"
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#include "gmp-impl.h"
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void
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mpz_clrbit (mpz_ptr d, mp_bitcnt_t bit_index)
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{
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mp_size_t dsize = d->_mp_size;
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mp_ptr dp = d->_mp_d;
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mp_size_t limb_index;
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limb_index = bit_index / GMP_NUMB_BITS;
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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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mp_limb_t dlimb;
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dlimb = dp[limb_index];
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dlimb &= ~((mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS));
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dp[limb_index] = dlimb;
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if (UNLIKELY (dlimb == 0 && limb_index == dsize-1))
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{
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/* high limb became zero, must normalize */
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do {
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dsize--;
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} while (dsize > 0 && dp[dsize-1] == 0);
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d->_mp_size = dsize;
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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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else
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{
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mp_size_t 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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dp[limb_index] |= (mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS);
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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 (UNLIKELY (d->_mp_alloc < limb_index + 1))
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dp = _mpz_realloc (d, limb_index + 1);
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MPN_ZERO (dp + dsize, limb_index - dsize);
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dp[limb_index] = (mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS);
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d->_mp_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_t) 1 << (bit_index % GMP_NUMB_BITS))) + 1)
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& GMP_NUMB_MASK);
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if (dp[limb_index] == 0)
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{
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mp_size_t i;
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for (i = limb_index + 1; i < dsize; i++)
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{
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dp[i] = (dp[i] + 1) & GMP_NUMB_MASK;
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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 (UNLIKELY (d->_mp_alloc < dsize))
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dp = _mpz_realloc (d, dsize);
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dp[i] = 1;
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d->_mp_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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