1 /* mpz_setbit -- set a specified bit. 2 3 Copyright 1991, 1993, 1994, 1995, 1997, 1999, 2001, 2002 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 the GNU Lesser General Public License as published by 10 the Free Software Foundation; either version 3 of the License, or (at your 11 option) any later version. 12 13 The GNU MP Library is distributed in the hope that it will be useful, but 14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 15 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 16 License for more details. 17 18 You should have received a copy of the GNU Lesser General Public License 19 along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */ 20 21 #include "gmp.h" 22 #include "gmp-impl.h" 23 24 void 25 mpz_setbit (mpz_ptr d, mp_bitcnt_t bit_index) 26 { 27 mp_size_t dsize = d->_mp_size; 28 mp_ptr dp = d->_mp_d; 29 mp_size_t limb_index; 30 31 limb_index = bit_index / GMP_NUMB_BITS; 32 if (dsize >= 0) 33 { 34 if (limb_index < dsize) 35 { 36 dp[limb_index] |= (mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS); 37 d->_mp_size = dsize; 38 } 39 else 40 { 41 /* Ugh. The bit should be set outside of the end of the 42 number. We have to increase the size of the number. */ 43 if (UNLIKELY (d->_mp_alloc < limb_index + 1)) 44 dp = _mpz_realloc (d, limb_index + 1); 45 MPN_ZERO (dp + dsize, limb_index - dsize); 46 dp[limb_index] = (mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS); 47 d->_mp_size = limb_index + 1; 48 } 49 } 50 else 51 { 52 mp_size_t zero_bound; 53 54 /* Simulate two's complement arithmetic, i.e. simulate 55 1. Set OP = ~(OP - 1) [with infinitely many leading ones]. 56 2. Set the bit. 57 3. Set OP = ~OP + 1. */ 58 59 dsize = -dsize; 60 61 /* No upper bound on this loop, we're sure there's a non-zero limb 62 sooner ot later. */ 63 for (zero_bound = 0; ; zero_bound++) 64 if (dp[zero_bound] != 0) 65 break; 66 67 if (limb_index > zero_bound) 68 { 69 if (limb_index < dsize) 70 { 71 mp_limb_t dlimb; 72 dlimb = dp[limb_index]; 73 dlimb &= ~((mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS)); 74 dp[limb_index] = dlimb; 75 76 if (UNLIKELY (dlimb == 0 && limb_index == dsize-1)) 77 { 78 /* high limb became zero, must normalize */ 79 do { 80 dsize--; 81 } while (dsize > 0 && dp[dsize-1] == 0); 82 d->_mp_size = -dsize; 83 } 84 } 85 } 86 else if (limb_index == zero_bound) 87 { 88 dp[limb_index] = ((dp[limb_index] - 1) 89 & ~((mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS))) + 1; 90 if (dp[limb_index] == 0) 91 { 92 mp_size_t i; 93 for (i = limb_index + 1; i < dsize; i++) 94 { 95 dp[i] += 1; 96 if (dp[i] != 0) 97 goto fin; 98 } 99 /* We got carry all way out beyond the end of D. Increase 100 its size (and allocation if necessary). */ 101 dsize++; 102 if (UNLIKELY (d->_mp_alloc < dsize)) 103 dp = _mpz_realloc (d, dsize); 104 dp[i] = 1; 105 d->_mp_size = -dsize; 106 fin:; 107 } 108 } 109 else 110 { 111 mpn_decr_u (dp + limb_index, 112 (mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS)); 113 dsize -= dp[dsize - 1] == 0; 114 d->_mp_size = -dsize; 115 } 116 } 117 } 118