contrib/gmp/mpz/setbit.c

   1 /* mpz_setbit -- set a specified bit.
   2
   3 Copyright 1991, 1993, 1994, 1995, 1997, 1999, 2001, 2002 Free Software
   4 Foundation, Inc.
   5
   6 This file is part of the GNU MP Library.
   7
   8 The GNU MP Library is free software; you can redistribute it and/or modify
   9 it under the terms of the GNU Lesser General Public License as published by
  10 the Free Software Foundation; either version 3 of the License, or (at your
  11 option) any later version.
  12
  13 The GNU MP Library is distributed in the hope that it will be useful, but
  14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  15 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  16 License for more details.
  17
  18 You should have received a copy of the GNU Lesser General Public License
  19 along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
  20
  21 #include "gmp.h"
  22 #include "gmp-impl.h"
  23
  24 void
  25 mpz_setbit (mpz_ptr d, mp_bitcnt_t bit_index)
  26 {
  27   mp_size_t dsize = d->_mp_size;
  28   mp_ptr dp = d->_mp_d;
  29   mp_size_t limb_index;
  30
  31   limb_index = bit_index / GMP_NUMB_BITS;
  32   if (dsize >= 0)
  33     {
  34       if (limb_index < dsize)
  35         {
  36           dp[limb_index] |= (mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS);
  37           d->_mp_size = dsize;
  38         }
  39       else
  40         {
  41           /* Ugh.  The bit should be set outside of the end of the
  42              number.  We have to increase the size of the number.  */
  43           if (UNLIKELY (d->_mp_alloc < limb_index + 1))
  44             dp = _mpz_realloc (d, limb_index + 1);
  45           MPN_ZERO (dp + dsize, limb_index - dsize);
  46           dp[limb_index] = (mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS);
  47           d->_mp_size = limb_index + 1;
  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. Set 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             {
  71               mp_limb_t  dlimb;
  72               dlimb = dp[limb_index];
  73               dlimb &= ~((mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS));
  74               dp[limb_index] = dlimb;
  75
  76               if (UNLIKELY (dlimb == 0 && limb_index == dsize-1))
  77                 {
  78                   /* high limb became zero, must normalize */
  79                   do {
  80                     dsize--;
  81                   } while (dsize > 0 && dp[dsize-1] == 0);
  82                   d->_mp_size = -dsize;
  83                 }
  84             }
  85         }
  86       else if (limb_index == zero_bound)
  87         {
  88           dp[limb_index] = ((dp[limb_index] - 1)
  89                             & ~((mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS))) + 1;
  90           if (dp[limb_index] == 0)
  91             {
  92               mp_size_t i;
  93               for (i = limb_index + 1; i < dsize; i++)
  94                 {
  95                   dp[i] += 1;
  96                   if (dp[i] != 0)
  97                     goto fin;
  98                 }
  99               /* We got carry all way out beyond the end of D.  Increase
 100                  its size (and allocation if necessary).  */
 101               dsize++;
 102               if (UNLIKELY (d->_mp_alloc < dsize))
 103                 dp = _mpz_realloc (d, dsize);
 104               dp[i] = 1;
 105               d->_mp_size = -dsize;
 106             fin:;
 107             }
 108         }
 109       else
 110         {
 111           mpn_decr_u (dp + limb_index,
 112                      (mp_limb_t) 1 << (bit_index % GMP_NUMB_BITS));
 113           dsize -= dp[dsize - 1] == 0;
 114           d->_mp_size = -dsize;
 115         }
 116     }
 117 }