setbit.c
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上传日期:2022-08-06
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文件大小:3k
- /* mpz_setbit -- set a specified bit.
- Copyright 1991, 1993, 1994, 1995, 1997, 1999, 2001, 2002 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_setbit (mpz_ptr d, mp_bitcnt_t bit_index)
- {
- mp_size_t dsize = d->_mp_size;
- mp_ptr dp = d->_mp_d;
- mp_size_t limb_index;
- limb_index = bit_index / GMP_NUMB_BITS;
- if (dsize >= 0)
- {
- if (limb_index < dsize)
- {
- dp[limb_index] |= (mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS);
- d->_mp_size = dsize;
- }
- else
- {
- /* Ugh. The bit should be set outside of the end of the
- number. We have to increase the size of the number. */
- if (UNLIKELY (d->_mp_alloc < limb_index + 1))
- dp = _mpz_realloc (d, limb_index + 1);
- MPN_ZERO (dp + dsize, limb_index - dsize);
- dp[limb_index] = (mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS);
- d->_mp_size = limb_index + 1;
- }
- }
- else
- {
- mp_size_t zero_bound;
- /* Simulate two's complement arithmetic, i.e. simulate
- 1. Set OP = ~(OP - 1) [with infinitely many leading ones].
- 2. Set the bit.
- 3. Set OP = ~OP + 1. */
- dsize = -dsize;
- /* No upper bound on this loop, we're sure there's a non-zero limb
- sooner ot later. */
- for (zero_bound = 0; ; zero_bound++)
- if (dp[zero_bound] != 0)
- break;
- if (limb_index > zero_bound)
- {
- if (limb_index < dsize)
- {
- mp_limb_t dlimb;
- dlimb = dp[limb_index];
- dlimb &= ~((mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS));
- dp[limb_index] = dlimb;
- if (UNLIKELY (dlimb == 0 && limb_index == dsize-1))
- {
- /* high limb became zero, must normalize */
- do {
- dsize--;
- } while (dsize > 0 && dp[dsize-1] == 0);
- d->_mp_size = -dsize;
- }
- }
- }
- else if (limb_index == zero_bound)
- {
- dp[limb_index] = ((dp[limb_index] - 1)
- & ~((mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS))) + 1;
- if (dp[limb_index] == 0)
- {
- mp_size_t i;
- for (i = limb_index + 1; i < dsize; i++)
- {
- dp[i] += 1;
- if (dp[i] != 0)
- goto fin;
- }
- /* We got carry all way out beyond the end of D. Increase
- its size (and allocation if necessary). */
- dsize++;
- if (UNLIKELY (d->_mp_alloc < dsize))
- dp = _mpz_realloc (d, dsize);
- dp[i] = 1;
- d->_mp_size = -dsize;
- fin:;
- }
- }
- else
- {
- mpn_decr_u (dp + limb_index,
- (mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS));
- dsize -= dp[dsize - 1] == 0;
- d->_mp_size = -dsize;
- }
- }
- }