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-impl.h"
      33  
      34  void
      35  mpz_setbit (mpz_ptr d, mp_bitcnt_t bit_idx)
      36  {
      37    mp_size_t dsize = SIZ (d);
      38    mp_ptr dp = PTR (d);
      39    mp_size_t limb_idx;
      40    mp_limb_t mask;
      41  
      42    limb_idx = bit_idx / GMP_NUMB_BITS;
      43    mask = CNST_LIMB(1) << (bit_idx % GMP_NUMB_BITS);
      44    if (dsize >= 0)
      45      {
      46        if (limb_idx < dsize)
      47  	{
      48  	  dp[limb_idx] |= mask;
      49  	}
      50        else
      51  	{
      52  	  /* Ugh.  The bit should be set outside of the end of the
      53  	     number.  We have to increase the size of the number.  */
      54  	  dp = MPZ_REALLOC (d, limb_idx + 1);
      55  	  SIZ (d) = limb_idx + 1;
      56  	  MPN_ZERO (dp + dsize, limb_idx - dsize);
      57  	  dp[limb_idx] = mask;
      58  	}
      59      }
      60    else
      61      {
      62        /* Simulate two's complement arithmetic, i.e. simulate
      63  	 1. Set OP = ~(OP - 1) [with infinitely many leading ones].
      64  	 2. Set the bit.
      65  	 3. Set OP = ~OP + 1.  */
      66  
      67        dsize = -dsize;
      68  
      69        if (limb_idx < dsize)
      70  	{
      71  	  mp_size_t zero_bound;
      72  	  /* No index upper bound on this loop, we're sure there's a non-zero limb
      73  	     sooner or later.  */
      74  	  zero_bound = 0;
      75  	  while (dp[zero_bound] == 0)
      76  	    zero_bound++;
      77  
      78  	  if (limb_idx > zero_bound)
      79  	    {
      80  	      mp_limb_t	 dlimb;
      81  	      dlimb = dp[limb_idx] & ~mask;
      82  	      dp[limb_idx] = dlimb;
      83  
      84  	      if (UNLIKELY ((dlimb == 0) + limb_idx == dsize)) /* dsize == limb_idx + 1 */
      85  		{
      86  		  /* high limb became zero, must normalize */
      87  		  MPN_NORMALIZE (dp, limb_idx);
      88  		  SIZ (d) = -limb_idx;
      89  		}
      90  	    }
      91  	  else if (limb_idx == zero_bound)
      92  	    {
      93  	      dp[limb_idx] = ((dp[limb_idx] - 1) & ~mask) + 1;
      94  	      ASSERT (dp[limb_idx] != 0);
      95  	    }
      96  	  else
      97  	    {
      98  	      MPN_DECR_U (dp + limb_idx, dsize - limb_idx, mask);
      99  	      dsize -= dp[dsize - 1] == 0;
     100  	      SIZ (d) = -dsize;
     101  	    }
     102  	}
     103      }
     104  }