diff options
Diffstat (limited to 'gnu/lib/libgmp/mpz_clrbit.c')
| -rw-r--r-- | gnu/lib/libgmp/mpz_clrbit.c | 124 |
1 files changed, 124 insertions, 0 deletions
diff --git a/gnu/lib/libgmp/mpz_clrbit.c b/gnu/lib/libgmp/mpz_clrbit.c new file mode 100644 index 0000000..7fde814 --- /dev/null +++ b/gnu/lib/libgmp/mpz_clrbit.c @@ -0,0 +1,124 @@ +/* mpz_clrbit -- clear a specified bit. + +Copyright (C) 1991 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 General Public License as published by +the Free Software Foundation; either version 2, 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 General Public License for more details. + +You should have received a copy of the GNU General Public License +along with the GNU MP Library; see the file COPYING. If not, write to +the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */ + +#include "gmp.h" +#include "gmp-impl.h" + +#define MPN_NORMALIZE(p, size) \ + do { \ + mp_size i; \ + for (i = (size) - 1; i >= 0; i--) \ + if ((p)[i] != 0) \ + break; \ + (size) = i + 1; \ + } while (0) + +void +#ifdef __STDC__ +mpz_clrbit (MP_INT *d, unsigned long int bit_index) +#else +mpz_clrbit (d, bit_index) + MP_INT *d; + unsigned long int bit_index; +#endif +{ + mp_size dsize = d->size; + mp_ptr dp = d->d; + mp_size limb_index; + + limb_index = bit_index / BITS_PER_MP_LIMB; + if (dsize >= 0) + { + if (limb_index < dsize) + { + dp[limb_index] &= ~((mp_limb) 1 << (bit_index % BITS_PER_MP_LIMB)); + MPN_NORMALIZE (dp, dsize); + d->size = dsize; + } + else + ; + } + else + { + mp_size zero_bound; + + /* Simulate two's complement arithmetic, i.e. simulate + 1. Set OP = ~(OP - 1) [with infinitely many leading ones]. + 2. clear the bit. + 3. Set OP = ~OP + 1. */ + + dsize = -dsize; + + /* No upper bound on this loop, we're sure there's a non-zero limb + sooner ot later. */ + for (zero_bound = 0; ; zero_bound++) + if (dp[zero_bound] != 0) + break; + + if (limb_index > zero_bound) + { + if (limb_index < dsize) + { + dp[limb_index] |= ((mp_limb) 1 << (bit_index % BITS_PER_MP_LIMB)); + } + else + { + /* Ugh. The bit should be cleared outside of the end of the + number. We have to increase the size of the number. */ + if (d->alloc < limb_index + 1) + { + _mpz_realloc (d, limb_index + 1); + dp = d->d; + } + MPN_ZERO (dp + dsize, limb_index - dsize); + dp[limb_index] = ((mp_limb) 1 << (bit_index % BITS_PER_MP_LIMB)); + d->size = -(limb_index + 1); + } + } + else if (limb_index == zero_bound) + { + dp[limb_index] = ((dp[limb_index] - 1) + | ((mp_limb) 1 << (bit_index % BITS_PER_MP_LIMB))) + 1; + if (dp[limb_index] == 0) + { + mp_size i; + for (i = limb_index + 1; i < dsize; i++) + { + dp[i] += 1; + if (dp[i] != 0) + goto fin; + } + /* We got carry all way out beyond the end of D. Increase + its size (and allocation if necessary). */ + dsize++; + if (d->alloc < dsize) + { + _mpz_realloc (d, dsize); + dp = d->d; + } + dp[i] = 1; + d->size = -dsize; + fin:; + } + } + else + ; + } +} |
