1/* mpz_rrandomb -- Generate a positive random mpz_t of specified bit size, with
2   long runs of consecutive ones and zeros in the binary representation.
3   Meant for testing of other MP routines.
4
5Copyright 2000, 2001, 2002, 2004 Free Software Foundation, Inc.
6
7This file is part of the GNU MP Library.
8
9The GNU MP Library is free software; you can redistribute it and/or modify
10it under the terms of the GNU Lesser General Public License as published by
11the Free Software Foundation; either version 3 of the License, or (at your
12option) any later version.
13
14The GNU MP Library is distributed in the hope that it will be useful, but
15WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
16or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
17License for more details.
18
19You should have received a copy of the GNU Lesser General Public License
20along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
21
22#include "gmp.h"
23#include "gmp-impl.h"
24
25static void gmp_rrandomb __GMP_PROTO ((mp_ptr, gmp_randstate_t, mp_bitcnt_t));
26
27void
28mpz_rrandomb (mpz_ptr x, gmp_randstate_t rstate, mp_bitcnt_t nbits)
29{
30  mp_size_t nl;
31
32  nl = (nbits + GMP_NUMB_BITS - 1) / GMP_NUMB_BITS;
33  if (nbits != 0)
34    {
35      MPZ_REALLOC (x, nl);
36      gmp_rrandomb (PTR(x), rstate, nbits);
37    }
38
39  SIZ(x) = nl;
40}
41
42/* Ask _gmp_rand for 32 bits per call unless that's more than a limb can hold.
43   Thus, we get the same random number sequence in the common cases.
44   FIXME: We should always generate the same random number sequence!  */
45#if GMP_NUMB_BITS < 32
46#define BITS_PER_RANDCALL GMP_NUMB_BITS
47#else
48#define BITS_PER_RANDCALL 32
49#endif
50
51static void
52gmp_rrandomb (mp_ptr rp, gmp_randstate_t rstate, mp_bitcnt_t nbits)
53{
54  mp_bitcnt_t bi;
55  mp_limb_t ranm;		/* buffer for random bits */
56  unsigned cap_chunksize, chunksize;
57  mp_size_t i;
58
59  /* Set entire result to 111..1  */
60  i = (nbits + GMP_NUMB_BITS - 1) / GMP_NUMB_BITS - 1;
61  rp[i] = GMP_NUMB_MAX >> (GMP_NUMB_BITS - (nbits % GMP_NUMB_BITS)) % GMP_NUMB_BITS;
62  for (i = i - 1; i >= 0; i--)
63    rp[i] = GMP_NUMB_MAX;
64
65  _gmp_rand (&ranm, rstate, BITS_PER_RANDCALL);
66  cap_chunksize = nbits / (ranm % 4 + 1);
67  cap_chunksize += cap_chunksize == 0; /* make it at least 1 */
68
69  bi = nbits;
70
71  for (;;)
72    {
73      _gmp_rand (&ranm, rstate, BITS_PER_RANDCALL);
74      chunksize = 1 + ranm % cap_chunksize;
75      bi = (bi < chunksize) ? 0 : bi - chunksize;
76
77      if (bi == 0)
78	break;			/* low chunk is ...1 */
79
80      rp[bi / GMP_NUMB_BITS] ^= CNST_LIMB (1) << bi % GMP_NUMB_BITS;
81
82      _gmp_rand (&ranm, rstate, BITS_PER_RANDCALL);
83      chunksize = 1 + ranm % cap_chunksize;
84      bi = (bi < chunksize) ? 0 : bi - chunksize;
85
86      mpn_incr_u (rp + bi / GMP_NUMB_BITS, CNST_LIMB (1) << bi % GMP_NUMB_BITS);
87
88      if (bi == 0)
89	break;			/* low chunk is ...0 */
90    }
91}
92