combit.c revision 1.1
1 1.1 mrg /* mpz_combit -- complement a specified bit. 2 1.1 mrg 3 1.1 mrg Copyright 2002, 2003 Free Software Foundation, Inc. 4 1.1 mrg 5 1.1 mrg This file is part of the GNU MP Library. 6 1.1 mrg 7 1.1 mrg The GNU MP Library is free software; you can redistribute it and/or modify 8 1.1 mrg it under the terms of the GNU Lesser General Public License as published by 9 1.1 mrg the Free Software Foundation; either version 3 of the License, or (at your 10 1.1 mrg option) any later version. 11 1.1 mrg 12 1.1 mrg The GNU MP Library is distributed in the hope that it will be useful, but 13 1.1 mrg WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 14 1.1 mrg or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 15 1.1 mrg License for more details. 16 1.1 mrg 17 1.1 mrg You should have received a copy of the GNU Lesser General Public License 18 1.1 mrg along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */ 19 1.1 mrg 20 1.1 mrg #include "gmp.h" 21 1.1 mrg #include "gmp-impl.h" 22 1.1 mrg 23 1.1 mrg void 24 1.1 mrg mpz_combit (mpz_ptr d, mp_bitcnt_t bit_index) 25 1.1 mrg { 26 1.1 mrg mp_size_t dsize = ABSIZ(d); 27 1.1 mrg mp_ptr dp = LIMBS(d); 28 1.1 mrg 29 1.1 mrg mp_size_t limb_index = bit_index / GMP_NUMB_BITS; 30 1.1 mrg mp_limb_t bit = ((mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS)); 31 1.1 mrg 32 1.1 mrg if (limb_index >= dsize) 33 1.1 mrg { 34 1.1 mrg MPZ_REALLOC(d, limb_index + 1); 35 1.1 mrg dp = LIMBS(d); 36 1.1 mrg 37 1.1 mrg MPN_ZERO(dp + dsize, limb_index + 1 - dsize); 38 1.1 mrg dsize = limb_index + 1; 39 1.1 mrg } 40 1.1 mrg 41 1.1 mrg if (SIZ(d) >= 0) 42 1.1 mrg { 43 1.1 mrg dp[limb_index] ^= bit; 44 1.1 mrg MPN_NORMALIZE (dp, dsize); 45 1.1 mrg SIZ(d) = dsize; 46 1.1 mrg } 47 1.1 mrg else 48 1.1 mrg { 49 1.1 mrg mp_limb_t x = -dp[limb_index]; 50 1.1 mrg mp_size_t i; 51 1.1 mrg 52 1.1 mrg /* non-zero limb below us means ones-complement */ 53 1.1 mrg for (i = limb_index-1; i >= 0; i--) 54 1.1 mrg if (dp[i] != 0) 55 1.1 mrg { 56 1.1 mrg x--; /* change twos comp to ones comp */ 57 1.1 mrg break; 58 1.1 mrg } 59 1.1 mrg 60 1.1 mrg if (x & bit) 61 1.1 mrg { 62 1.1 mrg mp_limb_t c; 63 1.1 mrg 64 1.1 mrg /* Clearing the bit increases the magitude. We might need a carry. */ 65 1.1 mrg MPZ_REALLOC(d, dsize + 1); 66 1.1 mrg dp = LIMBS(d); 67 1.1 mrg 68 1.1 mrg __GMPN_ADD_1 (c, dp+limb_index, dp+limb_index, 69 1.1 mrg dsize - limb_index, bit); 70 1.1 mrg dp[dsize] = c; 71 1.1 mrg dsize += c; 72 1.1 mrg } 73 1.1 mrg else 74 1.1 mrg /* Setting the bit decreases the magnitude */ 75 1.1 mrg mpn_sub_1(dp+limb_index, dp+limb_index, dsize + limb_index, bit); 76 1.1 mrg 77 1.1 mrg MPN_NORMALIZE (dp, dsize); 78 1.1 mrg SIZ(d) = -dsize; 79 1.1 mrg } 80 1.1 mrg } 81
Indexes created Sat Feb 28 05:31:39 UTC 2026