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Annotation of OpenXM_contrib/gmp/mpz/clrbit.c, Revision 1.1.1.3

1.1       maekawa     1: /* mpz_clrbit -- clear a specified bit.
                      2:
1.1.1.3 ! ohara       3: Copyright 1991, 1993, 1994, 1995, 2001, 2002 Free Software Foundation, Inc.
1.1       maekawa     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
1.1.1.2   maekawa     8: it under the terms of the GNU Lesser General Public License as published by
                      9: the Free Software Foundation; either version 2.1 of the License, or (at your
1.1       maekawa    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
1.1.1.2   maekawa    14: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
1.1       maekawa    15: License for more details.
                     16:
1.1.1.2   maekawa    17: You should have received a copy of the GNU Lesser General Public License
1.1       maekawa    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: mpz_clrbit (mpz_ptr d, unsigned long int bit_index)
                     27: {
                     28:   mp_size_t dsize = d->_mp_size;
                     29:   mp_ptr dp = d->_mp_d;
                     30:   mp_size_t limb_index;
                     31:
1.1.1.3 ! ohara      32:   limb_index = bit_index / GMP_NUMB_BITS;
1.1       maekawa    33:   if (dsize >= 0)
                     34:     {
                     35:       if (limb_index < dsize)
                     36:        {
1.1.1.3 ! ohara      37:          dp[limb_index] &= ~((mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS));
1.1       maekawa    38:          MPN_NORMALIZE (dp, dsize);
                     39:          d->_mp_size = dsize;
                     40:        }
                     41:       else
                     42:        ;
                     43:     }
                     44:   else
                     45:     {
                     46:       mp_size_t zero_bound;
                     47:
                     48:       /* Simulate two's complement arithmetic, i.e. simulate
                     49:         1. Set OP = ~(OP - 1) [with infinitely many leading ones].
                     50:         2. clear the bit.
                     51:         3. Set OP = ~OP + 1.  */
                     52:
                     53:       dsize = -dsize;
                     54:
                     55:       /* No upper bound on this loop, we're sure there's a non-zero limb
                     56:         sooner ot later.  */
                     57:       for (zero_bound = 0; ; zero_bound++)
                     58:        if (dp[zero_bound] != 0)
                     59:          break;
                     60:
                     61:       if (limb_index > zero_bound)
                     62:        {
                     63:          if (limb_index < dsize)
1.1.1.3 ! ohara      64:            dp[limb_index] |= (mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS);
1.1       maekawa    65:          else
                     66:            {
                     67:              /* Ugh.  The bit should be cleared outside of the end of the
                     68:                 number.  We have to increase the size of the number.  */
                     69:              if (d->_mp_alloc < limb_index + 1)
                     70:                {
                     71:                  _mpz_realloc (d, limb_index + 1);
                     72:                  dp = d->_mp_d;
                     73:                }
                     74:              MPN_ZERO (dp + dsize, limb_index - dsize);
1.1.1.3 ! ohara      75:              dp[limb_index] = (mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS);
1.1       maekawa    76:              d->_mp_size = -(limb_index + 1);
                     77:            }
                     78:        }
                     79:       else if (limb_index == zero_bound)
                     80:        {
1.1.1.3 ! ohara      81:          dp[limb_index] = ((((dp[limb_index] - 1)
        !            82:                              | ((mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS))) + 1)
        !            83:                            & GMP_NUMB_MASK);
1.1       maekawa    84:          if (dp[limb_index] == 0)
                     85:            {
                     86:              mp_size_t i;
                     87:              for (i = limb_index + 1; i < dsize; i++)
                     88:                {
1.1.1.3 ! ohara      89:                  dp[i] = (dp[i] + 1) & GMP_NUMB_MASK;
1.1       maekawa    90:                  if (dp[i] != 0)
                     91:                    goto fin;
                     92:                }
                     93:              /* We got carry all way out beyond the end of D.  Increase
                     94:                 its size (and allocation if necessary).  */
                     95:              dsize++;
                     96:              if (d->_mp_alloc < dsize)
                     97:                {
                     98:                  _mpz_realloc (d, dsize);
                     99:                  dp = d->_mp_d;
                    100:                }
                    101:              dp[i] = 1;
                    102:              d->_mp_size = -dsize;
                    103:            fin:;
                    104:            }
                    105:        }
                    106:       else
                    107:        ;
                    108:     }
                    109: }