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Annotation of OpenXM_contrib/gmp/mpz/clrbit.c, Revision 1.1

1.1     ! maekawa     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: }