| Austin Schuh | bb1338c | 2024-06-15 19:31:16 -0700 | [diff] [blame] | 1 | /* mpz_clrbit -- clear a specified bit. |
| 2 | |
| 3 | Copyright 1991, 1993-1995, 2001, 2002, 2012 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-impl.h" |
| 32 | |
| 33 | void |
| 34 | mpz_clrbit (mpz_ptr d, mp_bitcnt_t bit_idx) |
| 35 | { |
| 36 | mp_size_t dsize = SIZ (d); |
| 37 | mp_ptr dp = PTR (d); |
| 38 | mp_size_t limb_idx; |
| 39 | mp_limb_t mask; |
| 40 | |
| 41 | limb_idx = bit_idx / GMP_NUMB_BITS; |
| 42 | mask = CNST_LIMB(1) << (bit_idx % GMP_NUMB_BITS); |
| 43 | if (dsize >= 0) |
| 44 | { |
| 45 | if (limb_idx < dsize) |
| 46 | { |
| 47 | mp_limb_t dlimb; |
| 48 | dlimb = dp[limb_idx] & ~mask; |
| 49 | dp[limb_idx] = dlimb; |
| 50 | |
| 51 | if (UNLIKELY ((dlimb == 0) + limb_idx == dsize)) /* dsize == limb_idx + 1 */ |
| 52 | { |
| 53 | /* high limb became zero, must normalize */ |
| 54 | MPN_NORMALIZE (dp, limb_idx); |
| 55 | SIZ (d) = limb_idx; |
| 56 | } |
| 57 | } |
| 58 | else |
| 59 | ; |
| 60 | } |
| 61 | else |
| 62 | { |
| 63 | /* Simulate two's complement arithmetic, i.e. simulate |
| 64 | 1. Set OP = ~(OP - 1) [with infinitely many leading ones]. |
| 65 | 2. clear the bit. |
| 66 | 3. Set OP = ~OP + 1. */ |
| 67 | |
| 68 | dsize = -dsize; |
| 69 | |
| 70 | if (limb_idx < dsize) |
| 71 | { |
| 72 | mp_size_t zero_bound; |
| 73 | |
| 74 | /* No index upper bound on this loop, we're sure there's a non-zero limb |
| 75 | sooner or later. */ |
| 76 | zero_bound = 0; |
| 77 | while (dp[zero_bound] == 0) |
| 78 | zero_bound++; |
| 79 | |
| 80 | if (limb_idx > zero_bound) |
| 81 | { |
| 82 | dp[limb_idx] |= mask; |
| 83 | } |
| 84 | else if (limb_idx == zero_bound) |
| 85 | { |
| 86 | mp_limb_t dlimb; |
| 87 | dlimb = (((dp[limb_idx] - 1) | mask) + 1) & GMP_NUMB_MASK; |
| 88 | dp[limb_idx] = dlimb; |
| 89 | |
| 90 | if (dlimb == 0) |
| 91 | { |
| 92 | /* Increment at limb_idx + 1. Extend the number with a zero limb |
| 93 | for simplicity. */ |
| 94 | dp = MPZ_REALLOC (d, dsize + 1); |
| 95 | dp[dsize] = 0; |
| 96 | MPN_INCR_U (dp + limb_idx + 1, dsize - limb_idx, 1); |
| 97 | dsize += dp[dsize]; |
| 98 | |
| 99 | SIZ (d) = -dsize; |
| 100 | } |
| 101 | } |
| 102 | else |
| 103 | ; |
| 104 | } |
| 105 | else |
| 106 | { |
| 107 | /* Ugh. The bit should be cleared outside of the end of the |
| 108 | number. We have to increase the size of the number. */ |
| 109 | dp = MPZ_REALLOC (d, limb_idx + 1); |
| 110 | SIZ (d) = -(limb_idx + 1); |
| 111 | MPN_ZERO (dp + dsize, limb_idx - dsize); |
| 112 | dp[limb_idx] = mask; |
| 113 | } |
| 114 | } |
| 115 | } |