source/libs/gmp/gmp-src/mpz/setbit.c

   1 /* mpz_setbit -- set a specified bit.
   2
   3 Copyright 1991, 1993-1995, 1997, 1999, 2001, 2002, 2012 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 either:
  10
  11   * the GNU Lesser General Public License as published by the Free
  12     Software Foundation; either version 3 of the License, or (at your
  13     option) any later version.
  14
  15 or
  16
  17   * the GNU General Public License as published by the Free Software
  18     Foundation; either version 2 of the License, or (at your option) any
  19     later version.
  20
  21 or both in parallel, as here.
  22
  23 The GNU MP Library is distributed in the hope that it will be useful, but
  24 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  25 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  26 for more details.
  27
  28 You should have received copies of the GNU General Public License and the
  29 GNU Lesser General Public License along with the GNU MP Library.  If not,
  30 see https://www.gnu.org/licenses/.  */
  31
  32 #include "gmp.h"
  33 #include "gmp-impl.h"
  34
  35 void
  36 mpz_setbit (mpz_ptr d, mp_bitcnt_t bit_idx)
  37 {
  38   mp_size_t dsize = SIZ (d);
  39   mp_ptr dp = PTR (d);
  40   mp_size_t limb_idx;
  41   mp_limb_t mask;
  42
  43   limb_idx = bit_idx / GMP_NUMB_BITS;
  44   mask = CNST_LIMB(1) << (bit_idx % GMP_NUMB_BITS);
  45   if (dsize >= 0)
  46     {
  47       if (limb_idx < dsize)
  48         {
  49           dp[limb_idx] |= mask;
  50         }
  51       else
  52         {
  53           /* Ugh.  The bit should be set outside of the end of the
  54              number.  We have to increase the size of the number.  */
  55           dp = MPZ_REALLOC (d, limb_idx + 1);
  56           SIZ (d) = limb_idx + 1;
  57           MPN_ZERO (dp + dsize, limb_idx - dsize);
  58           dp[limb_idx] = mask;
  59         }
  60     }
  61   else
  62     {
  63       /* Simulate two's complement arithmetic, i.e. simulate
  64          1. Set OP = ~(OP - 1) [with infinitely many leading ones].
  65          2. Set the bit.
  66          3. Set OP = ~OP + 1.  */
  67
  68       dsize = -dsize;
  69
  70       if (limb_idx < dsize)
  71         {
  72           mp_size_t zero_bound;
  73           /* No index upper bound on this loop, we're sure there's a non-zero limb
  74              sooner or later.  */
  75           zero_bound = 0;
  76           while (dp[zero_bound] == 0)
  77             zero_bound++;
  78
  79           if (limb_idx > zero_bound)
  80             {
  81               mp_limb_t  dlimb;
  82               dlimb = dp[limb_idx] & ~mask;
  83               dp[limb_idx] = dlimb;
  84
  85               if (UNLIKELY ((dlimb == 0) + limb_idx == dsize)) /* dsize == limb_idx + 1 */
  86                 {
  87                   /* high limb became zero, must normalize */
  88                   MPN_NORMALIZE (dp, limb_idx);
  89                   SIZ (d) = -limb_idx;
  90                 }
  91             }
  92           else if (limb_idx == zero_bound)
  93             {
  94               dp[limb_idx] = ((dp[limb_idx] - 1) & ~mask) + 1;
  95               ASSERT (dp[limb_idx] != 0);
  96             }
  97           else
  98             {
  99               MPN_DECR_U (dp + limb_idx, dsize - limb_idx, mask);
 100               dsize -= dp[dsize - 1] == 0;
 101               SIZ (d) = -dsize;
 102             }
 103         }
 104     }
 105 }