1/* mpz_setbit -- set a specified bit.
2
3Copyright 1991, 1993, 1994, 1995, 1997, 1999, 2001, 2002 Free Software
4Foundation, Inc.
5
6This file is part of the GNU MP Library.
7
8The GNU MP Library is free software; you can redistribute it and/or modify
9it under the terms of the GNU Lesser General Public License as published by
10the Free Software Foundation; either version 3 of the License, or (at your
11option) any later version.
12
13The GNU MP Library is distributed in the hope that it will be useful, but
14WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
15or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
16License for more details.
17
18You should have received a copy of the GNU Lesser General Public License
19along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
20
21#include "gmp.h"
22#include "gmp-impl.h"
23
24void
25mpz_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}
118