3 * $Id: mprand.c,v 1.1 1999/12/10 23:23:05 mdw Exp $
5 * Generate a random multiprecision integer
7 * (c) 1999 Straylight/Edgeware
10 /*----- Licensing notice --------------------------------------------------*
12 * This file is part of Catacomb.
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.
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.
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,
30 /*----- Revision history --------------------------------------------------*
33 * Revision 1.1 1999/12/10 23:23:05 mdw
34 * Support for generating random large integers.
38 /*----- Header files ------------------------------------------------------*/
40 #include <mLib/alloc.h>
46 /*----- Main code ---------------------------------------------------------*/
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
55 * Returns: A random integer with the requested number of bits.
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.
64 mp
*mprand(mp
*d
, unsigned b
, grand
*r
, mpw
or)
66 size_t sz
= (b
+ 7) / 8;
67 octet
*v
= xmalloc(sz
);
70 /* --- Fill buffer with random data --- */
72 r
->ops
->fill(r
, v
, sz
);
74 /* --- Force into the correct range --- *
76 * This is slightly tricky. Oh, well.
81 v
[0] = (v
[0] & (m
- 1)) | m
;
83 /* --- Mask, load and return --- */
85 d
= mp_loadb(d
, v
, sz
);
91 /*----- That's all, folks -------------------------------------------------*/