1 /* mpz_setbit -- set a specified bit. 2 3 Copyright 1991, 1993-1995, 1997, 1999, 2001, 2002, 2012 Free Software 4 Foundation, Inc. 5 6 This file is part of the GNU MP Library. 7 8 The GNU MP Library is free software; you can redistribute it and/or modify 9 it under the terms of either: 10 11 * the GNU Lesser General Public License as published by the Free 12 Software Foundation; either version 3 of the License, or (at your 13 option) any later version. 14 15 or 16 17 * the GNU General Public License as published by the Free Software 18 Foundation; either version 2 of the License, or (at your option) any 19 later version. 20 21 or both in parallel, as here. 22 23 The GNU MP Library is distributed in the hope that it will be useful, but 24 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 25 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 26 for more details. 27 28 You should have received copies of the GNU General Public License and the 29 GNU Lesser General Public License along with the GNU MP Library. If not, 30 see https://www.gnu.org/licenses/. */ 31 32 #include "gmp.h" 33 #include "gmp-impl.h" 34 35 void 36 mpz_setbit (mpz_ptr d, mp_bitcnt_t bit_idx) 37 { 38 mp_size_t dsize = SIZ (d); 39 mp_ptr dp = PTR (d); 40 mp_size_t limb_idx; 41 mp_limb_t mask; 42 43 limb_idx = bit_idx / GMP_NUMB_BITS; 44 mask = CNST_LIMB(1) << (bit_idx % GMP_NUMB_BITS); 45 if (dsize >= 0) 46 { 47 if (limb_idx < dsize) 48 { 49 dp[limb_idx] |= mask; 50 } 51 else 52 { 53 /* Ugh. The bit should be set outside of the end of the 54 number. We have to increase the size of the number. */ 55 dp = MPZ_REALLOC (d, limb_idx + 1); 56 SIZ (d) = limb_idx + 1; 57 MPN_ZERO (dp + dsize, limb_idx - dsize); 58 dp[limb_idx] = mask; 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. Set 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 /* No index upper bound on this loop, we're sure there's a non-zero limb 74 sooner or later. */ 75 zero_bound = 0; 76 while (dp[zero_bound] == 0) 77 zero_bound++; 78 79 if (limb_idx > zero_bound) 80 { 81 mp_limb_t dlimb; 82 dlimb = dp[limb_idx] & ~mask; 83 dp[limb_idx] = dlimb; 84 85 if (UNLIKELY ((dlimb == 0) + limb_idx == dsize)) /* dsize == limb_idx + 1 */ 86 { 87 /* high limb became zero, must normalize */ 88 MPN_NORMALIZE (dp, limb_idx); 89 SIZ (d) = -limb_idx; 90 } 91 } 92 else if (limb_idx == zero_bound) 93 { 94 dp[limb_idx] = ((dp[limb_idx] - 1) & ~mask) + 1; 95 ASSERT (dp[limb_idx] != 0); 96 } 97 else 98 { 99 MPN_DECR_U (dp + limb_idx, dsize - limb_idx, mask); 100 dsize -= dp[dsize - 1] == 0; 101 SIZ (d) = -dsize; 102 } 103 } 104 } 105 } 106