| | 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 | |
| | 64 | mp *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 -------------------------------------------------*/ |
projects / u / mdw / catacomb / blame_incremental