1 1.1 mrg /* mpz_combit -- complement a specified bit. 2 1.1 mrg 3 1.1.1.3 mrg Copyright 2002, 2003, 2012, 2015 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 1.1.1.3 mrg it under the terms of either: 9 1.1.1.3 mrg 10 1.1.1.3 mrg * the GNU Lesser General Public License as published by the Free 11 1.1.1.3 mrg Software Foundation; either version 3 of the License, or (at your 12 1.1.1.3 mrg option) any later version. 13 1.1.1.3 mrg 14 1.1.1.3 mrg or 15 1.1.1.3 mrg 16 1.1.1.3 mrg * the GNU General Public License as published by the Free Software 17 1.1.1.3 mrg Foundation; either version 2 of the License, or (at your option) any 18 1.1.1.3 mrg later version. 19 1.1.1.3 mrg 20 1.1.1.3 mrg or both in parallel, as here. 21 1.1 mrg 22 1.1 mrg The GNU MP Library is distributed in the hope that it will be useful, but 23 1.1 mrg WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 24 1.1.1.3 mrg or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 25 1.1.1.3 mrg for more details. 26 1.1 mrg 27 1.1.1.3 mrg You should have received copies of the GNU General Public License and the 28 1.1.1.3 mrg GNU Lesser General Public License along with the GNU MP Library. If not, 29 1.1.1.3 mrg see https://www.gnu.org/licenses/. */ 30 1.1 mrg 31 1.1 mrg #include "gmp-impl.h" 32 1.1 mrg 33 1.1 mrg void 34 1.1 mrg mpz_combit (mpz_ptr d, mp_bitcnt_t bit_index) 35 1.1 mrg { 36 1.1.1.2 mrg mp_size_t dsize = SIZ(d); 37 1.1.1.2 mrg mp_ptr dp = PTR(d); 38 1.1 mrg 39 1.1 mrg mp_size_t limb_index = bit_index / GMP_NUMB_BITS; 40 1.1.1.2 mrg mp_limb_t bit = (CNST_LIMB (1) << (bit_index % GMP_NUMB_BITS)); 41 1.1 mrg 42 1.1.1.2 mrg /* Check for the most common case: Positive input, no realloc or 43 1.1.1.2 mrg normalization needed. */ 44 1.1.1.2 mrg if (limb_index + 1 < dsize) 45 1.1.1.2 mrg dp[limb_index] ^= bit; 46 1.1.1.2 mrg 47 1.1.1.2 mrg /* Check for the hairy case. d < 0, and we have all zero bits to the 48 1.1.1.2 mrg right of the bit to toggle. */ 49 1.1.1.3 mrg else if (limb_index < -dsize 50 1.1.1.3 mrg && (limb_index == 0 || mpn_zero_p (dp, limb_index)) 51 1.1.1.2 mrg && (dp[limb_index] & (bit - 1)) == 0) 52 1.1 mrg { 53 1.1.1.2 mrg ASSERT (dsize < 0); 54 1.1.1.2 mrg dsize = -dsize; 55 1.1 mrg 56 1.1.1.2 mrg if (dp[limb_index] & bit) 57 1.1.1.2 mrg { 58 1.1.1.2 mrg /* We toggle the least significant one bit. Corresponds to 59 1.1.1.2 mrg an add, with potential carry propagation, on the absolute 60 1.1.1.2 mrg value. */ 61 1.1.1.2 mrg dp = MPZ_REALLOC (d, 1 + dsize); 62 1.1.1.2 mrg dp[dsize] = 0; 63 1.1.1.2 mrg MPN_INCR_U (dp + limb_index, 1 + dsize - limb_index, bit); 64 1.1.1.3 mrg SIZ(d) = - dsize - dp[dsize]; 65 1.1.1.2 mrg } 66 1.1.1.2 mrg else 67 1.1.1.2 mrg { 68 1.1.1.2 mrg /* We toggle a zero bit, subtract from the absolute value. */ 69 1.1.1.2 mrg MPN_DECR_U (dp + limb_index, dsize - limb_index, bit); 70 1.1.1.3 mrg /* The absolute value shrinked by at most one bit. */ 71 1.1.1.3 mrg dsize -= dp[dsize - 1] == 0; 72 1.1.1.3 mrg ASSERT (dsize > 0 && dp[dsize - 1] != 0); 73 1.1.1.3 mrg SIZ (d) = -dsize; 74 1.1.1.2 mrg } 75 1.1 mrg } 76 1.1 mrg else 77 1.1 mrg { 78 1.1.1.2 mrg /* Simple case: Toggle the bit in the absolute value. */ 79 1.1.1.2 mrg dsize = ABS(dsize); 80 1.1.1.2 mrg if (limb_index < dsize) 81 1.1 mrg { 82 1.1.1.3 mrg mp_limb_t dlimb; 83 1.1.1.3 mrg dlimb = dp[limb_index] ^ bit; 84 1.1.1.3 mrg dp[limb_index] = dlimb; 85 1.1 mrg 86 1.1.1.2 mrg /* Can happen only when limb_index = dsize - 1. Avoid SIZ(d) 87 1.1.1.2 mrg bookkeeping in the common case. */ 88 1.1.1.3 mrg if (UNLIKELY ((dlimb == 0) + limb_index == dsize)) /* dsize == limb_index + 1 */ 89 1.1.1.2 mrg { 90 1.1.1.3 mrg /* high limb became zero, must normalize */ 91 1.1.1.3 mrg MPN_NORMALIZE (dp, limb_index); 92 1.1.1.3 mrg SIZ (d) = SIZ (d) >= 0 ? limb_index : -limb_index; 93 1.1.1.2 mrg } 94 1.1 mrg } 95 1.1 mrg else 96 1.1.1.2 mrg { 97 1.1.1.2 mrg dp = MPZ_REALLOC (d, limb_index + 1); 98 1.1.1.2 mrg MPN_ZERO(dp + dsize, limb_index - dsize); 99 1.1.1.2 mrg dp[limb_index++] = bit; 100 1.1.1.2 mrg SIZ(d) = SIZ(d) >= 0 ? limb_index : -limb_index; 101 1.1.1.2 mrg } 102 1.1 mrg } 103 1.1 mrg } 104
Indexes created Sat Feb 28 05:31:39 UTC 2026