1 /* mpz_combit -- complement a specified bit. 2 3 Copyright 2002, 2003, 2012, 2015 Free Software Foundation, Inc. 4 5 This file is part of the GNU MP Library. 6 7 The GNU MP Library is free software; you can redistribute it and/or modify 8 it under the terms of either: 9 10 * the GNU Lesser General Public License as published by the Free 11 Software Foundation; either version 3 of the License, or (at your 12 option) any later version. 13 14 or 15 16 * the GNU General Public License as published by the Free Software 17 Foundation; either version 2 of the License, or (at your option) any 18 later version. 19 20 or both in parallel, as here. 21 22 The GNU MP Library is distributed in the hope that it will be useful, but 23 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 24 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 25 for more details. 26 27 You should have received copies of the GNU General Public License and the 28 GNU Lesser General Public License along with the GNU MP Library. If not, 29 see https://www.gnu.org/licenses/. */ 30 31 #include "gmp.h" 32 #include "gmp-impl.h" 33 34 void 35 mpz_combit (mpz_ptr d, mp_bitcnt_t bit_index) 36 { 37 mp_size_t dsize = SIZ(d); 38 mp_ptr dp = PTR(d); 39 40 mp_size_t limb_index = bit_index / GMP_NUMB_BITS; 41 mp_limb_t bit = (CNST_LIMB (1) << (bit_index % GMP_NUMB_BITS)); 42 43 /* Check for the most common case: Positive input, no realloc or 44 normalization needed. */ 45 if (limb_index + 1 < dsize) 46 dp[limb_index] ^= bit; 47 48 /* Check for the hairy case. d < 0, and we have all zero bits to the 49 right of the bit to toggle. */ 50 else if (limb_index < -dsize 51 && (limb_index == 0 || mpn_zero_p (dp, limb_index)) 52 && (dp[limb_index] & (bit - 1)) == 0) 53 { 54 ASSERT (dsize < 0); 55 dsize = -dsize; 56 57 if (dp[limb_index] & bit) 58 { 59 /* We toggle the least significant one bit. Corresponds to 60 an add, with potential carry propagation, on the absolute 61 value. */ 62 dp = MPZ_REALLOC (d, 1 + dsize); 63 dp[dsize] = 0; 64 MPN_INCR_U (dp + limb_index, 1 + dsize - limb_index, bit); 65 SIZ(d) = - dsize - dp[dsize]; 66 } 67 else 68 { 69 /* We toggle a zero bit, subtract from the absolute value. */ 70 MPN_DECR_U (dp + limb_index, dsize - limb_index, bit); 71 /* The absolute value shrinked by at most one bit. */ 72 dsize -= dp[dsize - 1] == 0; 73 ASSERT (dsize > 0 && dp[dsize - 1] != 0); 74 SIZ (d) = -dsize; 75 } 76 } 77 else 78 { 79 /* Simple case: Toggle the bit in the absolute value. */ 80 dsize = ABS(dsize); 81 if (limb_index < dsize) 82 { 83 mp_limb_t dlimb; 84 dlimb = dp[limb_index] ^ bit; 85 dp[limb_index] = dlimb; 86 87 /* Can happen only when limb_index = dsize - 1. Avoid SIZ(d) 88 bookkeeping in the common case. */ 89 if (UNLIKELY ((dlimb == 0) + limb_index == dsize)) /* dsize == limb_index + 1 */ 90 { 91 /* high limb became zero, must normalize */ 92 MPN_NORMALIZE (dp, limb_index); 93 SIZ (d) = SIZ (d) >= 0 ? limb_index : -limb_index; 94 } 95 } 96 else 97 { 98 dp = MPZ_REALLOC (d, limb_index + 1); 99 MPN_ZERO(dp + dsize, limb_index - dsize); 100 dp[limb_index++] = bit; 101 SIZ(d) = SIZ(d) >= 0 ? limb_index : -limb_index; 102 } 103 } 104 } 105