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Annotation of OpenXM/src/kan96xx/gmp-2.0.2-ssh-2/mpz/clrbit.c, Revision 1.1.1.1

1.1       takayama    1: /* mpz_clrbit -- clear a specified bit.
                      2:
                      3: Copyright (C) 1991, 1993, 1994, 1995 Free Software Foundation, Inc.
                      4:
                      5: This file is part of the GNU MP Library.
                      6:
                      7: The GNU MP Library is free software; you can redistribute it and/or modify
                      8: it under the terms of the GNU Library General Public License as published by
                      9: the Free Software Foundation; either version 2 of the License, or (at your
                     10: option) any later version.
                     11:
                     12: The GNU MP Library is distributed in the hope that it will be useful, but
                     13: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
                     14: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
                     15: License for more details.
                     16:
                     17: You should have received a copy of the GNU Library General Public License
                     18: along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
                     19: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
                     20: MA 02111-1307, USA. */
                     21:
                     22: #include "gmp.h"
                     23: #include "gmp-impl.h"
                     24:
                     25: void
                     26: #if __STDC__
                     27: mpz_clrbit (mpz_ptr d, unsigned long int bit_index)
                     28: #else
                     29: mpz_clrbit (d, bit_index)
                     30:      mpz_ptr d;
                     31:      unsigned long int bit_index;
                     32: #endif
                     33: {
                     34:   mp_size_t dsize = d->_mp_size;
                     35:   mp_ptr dp = d->_mp_d;
                     36:   mp_size_t limb_index;
                     37:
                     38:   limb_index = bit_index / BITS_PER_MP_LIMB;
                     39:   if (dsize >= 0)
                     40:     {
                     41:       if (limb_index < dsize)
                     42:        {
                     43:          dp[limb_index] &= ~((mp_limb_t) 1 << (bit_index % BITS_PER_MP_LIMB));
                     44:          MPN_NORMALIZE (dp, dsize);
                     45:          d->_mp_size = dsize;
                     46:        }
                     47:       else
                     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. clear 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:            dp[limb_index] |= (mp_limb_t) 1 << (bit_index % BITS_PER_MP_LIMB);
                     71:          else
                     72:            {
                     73:              /* Ugh.  The bit should be cleared outside of the end of the
                     74:                 number.  We have to increase the size of the number.  */
                     75:              if (d->_mp_alloc < limb_index + 1)
                     76:                {
                     77:                  _mpz_realloc (d, limb_index + 1);
                     78:                  dp = d->_mp_d;
                     79:                }
                     80:              MPN_ZERO (dp + dsize, limb_index - dsize);
                     81:              dp[limb_index] = (mp_limb_t) 1 << (bit_index % BITS_PER_MP_LIMB);
                     82:              d->_mp_size = -(limb_index + 1);
                     83:            }
                     84:        }
                     85:       else if (limb_index == zero_bound)
                     86:        {
                     87:          dp[limb_index] = ((dp[limb_index] - 1)
                     88:                            | ((mp_limb_t) 1 << (bit_index % BITS_PER_MP_LIMB))) + 1;
                     89:          if (dp[limb_index] == 0)
                     90:            {
                     91:              mp_size_t i;
                     92:              for (i = limb_index + 1; i < dsize; i++)
                     93:                {
                     94:                  dp[i] += 1;
                     95:                  if (dp[i] != 0)
                     96:                    goto fin;
                     97:                }
                     98:              /* We got carry all way out beyond the end of D.  Increase
                     99:                 its size (and allocation if necessary).  */
                    100:              dsize++;
                    101:              if (d->_mp_alloc < dsize)
                    102:                {
                    103:                  _mpz_realloc (d, dsize);
                    104:                  dp = d->_mp_d;
                    105:                }
                    106:              dp[i] = 1;
                    107:              d->_mp_size = -dsize;
                    108:            fin:;
                    109:            }
                    110:        }
                    111:       else
                    112:        ;
                    113:     }
                    114: }