1/* mpz_setbit -- set a specified bit. 2 3Copyright 1991, 1993, 1994, 1995, 1997, 1999, 2001, 2002 Free Software 4Foundation, Inc. 5 6This file is part of the GNU MP Library. 7 8The GNU MP Library is free software; you can redistribute it and/or modify 9it under the terms of the GNU Lesser General Public License as published by 10the Free Software Foundation; either version 3 of the License, or (at your 11option) any later version. 12 13The GNU MP Library is distributed in the hope that it will be useful, but 14WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 15or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 16License for more details. 17 18You should have received a copy of the GNU Lesser General Public License 19along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */ 20 21#include "gmp.h" 22#include "gmp-impl.h" 23 24void 25mpz_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