combit.c revision 1.1.1.2
1 1.1 mrg /* mpz_combit -- complement a specified bit. 2 1.1 mrg 3 1.1.1.2 mrg Copyright 2002, 2003, 2012 Free Software Foundation, Inc. 4 1.1 mrg 5 1.1 mrg This file is part of the GNU MP Library. 6 1.1 mrg 7 1.1 mrg The GNU MP Library is free software; you can redistribute it and/or modify 8 1.1 mrg it under the terms of the GNU Lesser General Public License as published by 9 1.1 mrg the Free Software Foundation; either version 3 of the License, or (at your 10 1.1 mrg option) any later version. 11 1.1 mrg 12 1.1 mrg The GNU MP Library is distributed in the hope that it will be useful, but 13 1.1 mrg WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 14 1.1 mrg or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 15 1.1 mrg License for more details. 16 1.1 mrg 17 1.1 mrg You should have received a copy of the GNU Lesser General Public License 18 1.1 mrg along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */ 19 1.1 mrg 20 1.1 mrg #include "gmp.h" 21 1.1 mrg #include "gmp-impl.h" 22 1.1 mrg 23 1.1 mrg void 24 1.1 mrg mpz_combit (mpz_ptr d, mp_bitcnt_t bit_index) 25 1.1 mrg { 26 1.1.1.2 mrg mp_size_t dsize = SIZ(d); 27 1.1.1.2 mrg mp_ptr dp = PTR(d); 28 1.1 mrg 29 1.1 mrg mp_size_t limb_index = bit_index / GMP_NUMB_BITS; 30 1.1.1.2 mrg mp_limb_t bit = (CNST_LIMB (1) << (bit_index % GMP_NUMB_BITS)); 31 1.1 mrg 32 1.1.1.2 mrg /* Check for the most common case: Positive input, no realloc or 33 1.1.1.2 mrg normalization needed. */ 34 1.1.1.2 mrg if (limb_index + 1 < dsize) 35 1.1.1.2 mrg dp[limb_index] ^= bit; 36 1.1.1.2 mrg 37 1.1.1.2 mrg /* Check for the hairy case. d < 0, and we have all zero bits to the 38 1.1.1.2 mrg right of the bit to toggle. */ 39 1.1.1.2 mrg else if (limb_index < -dsize && mpn_zero_p (dp, limb_index) 40 1.1.1.2 mrg && (dp[limb_index] & (bit - 1)) == 0) 41 1.1 mrg { 42 1.1.1.2 mrg ASSERT (dsize < 0); 43 1.1.1.2 mrg dsize = -dsize; 44 1.1 mrg 45 1.1.1.2 mrg if (dp[limb_index] & bit) 46 1.1.1.2 mrg { 47 1.1.1.2 mrg /* We toggle the least significant one bit. Corresponds to 48 1.1.1.2 mrg an add, with potential carry propagation, on the absolute 49 1.1.1.2 mrg value. */ 50 1.1.1.2 mrg dp = MPZ_REALLOC (d, 1 + dsize); 51 1.1.1.2 mrg dp[dsize] = 0; 52 1.1.1.2 mrg MPN_INCR_U (dp + limb_index, 1 + dsize - limb_index, bit); 53 1.1.1.2 mrg SIZ(d) -= dp[dsize]; 54 1.1.1.2 mrg } 55 1.1.1.2 mrg else 56 1.1.1.2 mrg { 57 1.1.1.2 mrg /* We toggle a zero bit, subtract from the absolute value. */ 58 1.1.1.2 mrg MPN_DECR_U (dp + limb_index, dsize - limb_index, bit); 59 1.1.1.2 mrg MPN_NORMALIZE (dp, dsize); 60 1.1.1.2 mrg ASSERT (dsize > 0); 61 1.1.1.2 mrg SIZ(d) = -dsize; 62 1.1.1.2 mrg } 63 1.1 mrg } 64 1.1 mrg else 65 1.1 mrg { 66 1.1.1.2 mrg /* Simple case: Toggle the bit in the absolute value. */ 67 1.1.1.2 mrg dsize = ABS(dsize); 68 1.1.1.2 mrg if (limb_index < dsize) 69 1.1 mrg { 70 1.1.1.2 mrg dp[limb_index] ^= bit; 71 1.1 mrg 72 1.1.1.2 mrg /* Can happen only when limb_index = dsize - 1. Avoid SIZ(d) 73 1.1.1.2 mrg bookkeeping in the common case. */ 74 1.1.1.2 mrg if (dp[dsize-1] == 0) 75 1.1.1.2 mrg { 76 1.1.1.2 mrg dsize--; 77 1.1.1.2 mrg MPN_NORMALIZE (dp, dsize); 78 1.1.1.2 mrg SIZ (d) = SIZ (d) >= 0 ? dsize : -dsize; 79 1.1.1.2 mrg } 80 1.1 mrg } 81 1.1 mrg else 82 1.1.1.2 mrg { 83 1.1.1.2 mrg dp = MPZ_REALLOC (d, limb_index + 1); 84 1.1.1.2 mrg MPN_ZERO(dp + dsize, limb_index - dsize); 85 1.1.1.2 mrg dp[limb_index++] = bit; 86 1.1.1.2 mrg SIZ(d) = SIZ(d) >= 0 ? limb_index : -limb_index; 87 1.1.1.2 mrg } 88 1.1 mrg } 89 1.1 mrg } 90
Indexes created Sat Feb 28 05:31:39 UTC 2026