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.
5 Copyright 2000, 2001, 2002, 2004 Free Software Foundation, Inc.
7 This file is part of the GNU MP Library.
9 The GNU MP Library is free software; you can redistribute it and/or modify
10 it under the terms of the GNU Lesser General Public License as published by
11 the Free Software Foundation; either version 3 of the License, or (at your
12 option) any later version.
14 The GNU MP Library is distributed in the hope that it will be useful, but
15 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
16 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
17 License for more details.
19 You should have received a copy of the GNU Lesser General Public License
20 along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
25 static void gmp_rrandomb __GMP_PROTO ((mp_ptr, gmp_randstate_t, unsigned long int));
28 mpz_rrandomb (mpz_ptr x, gmp_randstate_t rstate, unsigned long int nbits)
32 nl = (nbits + GMP_NUMB_BITS - 1) / GMP_NUMB_BITS;
36 gmp_rrandomb (PTR(x), rstate, nbits);
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
48 #define BITS_PER_RANDCALL 32
52 gmp_rrandomb (mp_ptr rp, gmp_randstate_t rstate, unsigned long int nbits)
55 mp_limb_t ranm; /* buffer for random bits */
56 unsigned cap_chunksize, chunksize;
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--)
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 */
73 _gmp_rand (&ranm, rstate, BITS_PER_RANDCALL);
74 chunksize = 1 + ranm % cap_chunksize;
75 bi = (bi < chunksize) ? 0 : bi - chunksize;
78 break; /* low chunk is ...1 */
80 rp[bi / GMP_NUMB_BITS] ^= CNST_LIMB (1) << bi % GMP_NUMB_BITS;
82 _gmp_rand (&ranm, rstate, BITS_PER_RANDCALL);
83 chunksize = 1 + ranm % cap_chunksize;
84 bi = (bi < chunksize) ? 0 : bi - chunksize;
86 mpn_incr_u (rp + bi / GMP_NUMB_BITS, CNST_LIMB (1) << bi % GMP_NUMB_BITS);
89 break; /* low chunk is ...0 */