| /* mpz_combit -- complement a specified bit. |
| |
| Copyright 2002, 2003 Free Software Foundation, Inc. |
| |
| This file is part of the GNU MP Library. |
| |
| The GNU MP Library is free software; you can redistribute it and/or modify |
| it under the terms of the GNU Lesser General Public License as published by |
| the Free Software Foundation; either version 3 of the License, or (at your |
| option) any later version. |
| |
| The GNU MP Library is distributed in the hope that it will be useful, but |
| WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY |
| or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public |
| License for more details. |
| |
| You should have received a copy of the GNU Lesser General Public License |
| along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */ |
| |
| #include "gmp.h" |
| #include "gmp-impl.h" |
| |
| void |
| mpz_combit (mpz_ptr d, unsigned long int bit_index) |
| { |
| mp_size_t dsize = ABSIZ(d); |
| mp_ptr dp = LIMBS(d); |
| |
| mp_size_t limb_index = bit_index / GMP_NUMB_BITS; |
| mp_limb_t bit = ((mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS)); |
| |
| if (limb_index >= dsize) |
| { |
| MPZ_REALLOC(d, limb_index + 1); |
| dp = LIMBS(d); |
| |
| MPN_ZERO(dp + dsize, limb_index + 1 - dsize); |
| dsize = limb_index + 1; |
| } |
| |
| if (SIZ(d) >= 0) |
| { |
| dp[limb_index] ^= bit; |
| MPN_NORMALIZE (dp, dsize); |
| SIZ(d) = dsize; |
| } |
| else |
| { |
| mp_limb_t x = -dp[limb_index]; |
| mp_size_t i; |
| |
| /* non-zero limb below us means ones-complement */ |
| for (i = limb_index-1; i >= 0; i--) |
| if (dp[i] != 0) |
| { |
| x--; /* change twos comp to ones comp */ |
| break; |
| } |
| |
| if (x & bit) |
| { |
| mp_limb_t c; |
| |
| /* Clearing the bit increases the magitude. We might need a carry. */ |
| MPZ_REALLOC(d, dsize + 1); |
| dp = LIMBS(d); |
| |
| __GMPN_ADD_1 (c, dp+limb_index, dp+limb_index, |
| dsize - limb_index, bit); |
| dp[dsize] = c; |
| dsize += c; |
| } |
| else |
| /* Setting the bit decreases the magnitude */ |
| mpn_sub_1(dp+limb_index, dp+limb_index, dsize + limb_index, bit); |
| |
| MPN_NORMALIZE (dp, dsize); |
| SIZ(d) = -dsize; |
| } |
| } |