Adjust Karatsuba parameters.
[u/mdw/catacomb] / mprand.c
CommitLineData
893c6259 1/* -*-c-*-
2 *
3 * $Id: mprand.c,v 1.1 1999/12/10 23:23:05 mdw Exp $
4 *
5 * Generate a random multiprecision integer
6 *
7 * (c) 1999 Straylight/Edgeware
8 */
9
10/*----- Licensing notice --------------------------------------------------*
11 *
12 * This file is part of Catacomb.
13 *
14 * Catacomb is free software; you can redistribute it and/or modify
15 * it under the terms of the GNU Library General Public License as
16 * published by the Free Software Foundation; either version 2 of the
17 * License, or (at your option) any later version.
18 *
19 * Catacomb is distributed in the hope that it will be useful,
20 * but WITHOUT ANY WARRANTY; without even the implied warranty of
21 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
22 * GNU Library General Public License for more details.
23 *
24 * You should have received a copy of the GNU Library General Public
25 * License along with Catacomb; if not, write to the Free
26 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
27 * MA 02111-1307, USA.
28 */
29
30/*----- Revision history --------------------------------------------------*
31 *
32 * $Log: mprand.c,v $
33 * Revision 1.1 1999/12/10 23:23:05 mdw
34 * Support for generating random large integers.
35 *
36 */
37
38/*----- Header files ------------------------------------------------------*/
39
40#include <mLib/alloc.h>
41
42#include "grand.h"
43#include "mp.h"
44#include "mprand.h"
45
46/*----- Main code ---------------------------------------------------------*/
47
48/* --- @mprand@ --- *
49 *
50 * Arguments: @mp *d@ = destination integer
51 * @unsigned b@ = number of bits
52 * @grand *r@ = pointer to random number source
53 * @mpw or@ = mask to OR with low-order bits
54 *
55 * Returns: A random integer with the requested number of bits.
56 *
57 * Use: Constructs an arbitrarily large pseudorandom integer.
58 * Assuming that the generator @r@ is good, the result is
59 * uniformly distributed in the interval %$[2^{b - 1}, 2^b)$%.
60 * The result is then ORred with the given @or@ value. This
61 * will often be 1, to make the result odd.
62 */
63
64mp *mprand(mp *d, unsigned b, grand *r, mpw or)
65{
66 size_t sz = (b + 7) / 8;
67 octet *v = xmalloc(sz);
68 unsigned m;
69
70 /* --- Fill buffer with random data --- */
71
72 r->ops->fill(r, v, sz);
73
74 /* --- Force into the correct range --- *
75 *
76 * This is slightly tricky. Oh, well.
77 */
78
79 b = (b - 1) % 8;
80 m = (1 << b);
81 v[0] = (v[0] & (m - 1)) | m;
82
83 /* --- Mask, load and return --- */
84
85 d = mp_loadb(d, v, sz);
86 d->v[0] |= or;
87 free(v);
88 return (d);
89}
90
91/*----- That's all, folks -------------------------------------------------*/