+++ /dev/null
-/* -*-c-*-
- *
- * $Id: mprand.c,v 1.5 2004/04/08 01:36:15 mdw Exp $
- *
- * Generate a random multiprecision integer
- *
- * (c) 1999 Straylight/Edgeware
- */
-
-/*----- Licensing notice --------------------------------------------------*
- *
- * This file is part of Catacomb.
- *
- * Catacomb is free software; you can redistribute it and/or modify
- * it under the terms of the GNU Library General Public License as
- * published by the Free Software Foundation; either version 2 of the
- * License, or (at your option) any later version.
- *
- * Catacomb is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU Library General Public License for more details.
- *
- * You should have received a copy of the GNU Library General Public
- * License along with Catacomb; if not, write to the Free
- * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
- * MA 02111-1307, USA.
- */
-
-/*----- Header files ------------------------------------------------------*/
-
-#include <mLib/alloc.h>
-
-#include "grand.h"
-#include "mp.h"
-#include "mprand.h"
-
-/*----- Main code ---------------------------------------------------------*/
-
-/* --- @mprand@ --- *
- *
- * Arguments: @mp *d@ = destination integer
- * @unsigned b@ = number of bits
- * @grand *r@ = pointer to random number source
- * @mpw or@ = mask to OR with low-order bits
- *
- * Returns: A random integer with the requested number of bits.
- *
- * Use: Constructs an arbitrarily large pseudorandom integer.
- * Assuming that the generator @r@ is good, the result is
- * uniformly distributed in the interval %$[2^{b - 1}, 2^b)$%.
- * The result is then ORred with the given @or@ value. This
- * will often be 1, to make the result odd.
- */
-
-mp *mprand(mp *d, unsigned b, grand *r, mpw or)
-{
- size_t sz = (b + 7) >> 3;
- arena *a = (d && (d->f & MP_BURN)) ? arena_secure : arena_global;
- octet *v = x_alloc(a, sz);
- unsigned m;
-
- /* --- Fill buffer with random data --- */
-
- r->ops->fill(r, v, sz);
-
- /* --- Force into the correct range --- *
- *
- * This is slightly tricky. Oh, well.
- */
-
- b = (b - 1) & 7;
- m = (1 << b);
- v[0] = (v[0] & (m - 1)) | m;
-
- /* --- Mask, load and return --- */
-
- d = mp_loadb(d, v, sz);
- d->v[0] |= or;
- memset(v, 0, sz);
- x_free(a, v);
- return (d);
-}
-
-/* --- @mprand_range@ --- *
- *
- * Arguments: @mp *d@ = destination integer
- * @mp *l@ = limit for random number
- * @grand *r@ = random number source
- * @mpw or@ = mask for low-order bits
- *
- * Returns: A pseudorandom integer, unformly distributed over the
- * interval %$[0, l)$%.
- *
- * Use: Generates a uniformly-distributed pseudorandom number in the
- * appropriate range.
- */
-
-mp *mprand_range(mp *d, mp *l, grand *r, mpw or)
-{
- size_t b = mp_bits(l);
- size_t sz = (b + 7) >> 3;
- arena *a = (d && (d->f & MP_BURN)) ? arena_secure : arena_global;
- octet *v = x_alloc(a, sz);
- unsigned m;
-
- /* --- The algorithm --- *
- *
- * Rather simpler than most. Find the number of bits in the number %$l$%
- * (i.e., the integer %$b$% such that %$2^{b - 1} \le l < 2^b$%), and
- * generate pseudorandom integers with %$n$% bits (but not, unlike in the
- * function above, with the top bit forced to 1). If the integer is
- * greater than or equal to %$l$%, try again.
- *
- * This is similar to the algorithms used in @lcrand_range@ and friends,
- * except that I've forced the `raw' range of the random numbers such that
- * %$l$% itself is the largest multiple of %$l$% in the range (since, by
- * the inequality above, %$2^b \le 2l$%). This removes the need for costly
- * division and remainder operations.
- *
- * As usual, the number of iterations expected is two.
- */
-
- b = ((b - 1) & 7) + 1;
- m = (1 << b) - 1;
- do {
- r->ops->fill(r, v, sz);
- v[0] &= m;
- d = mp_loadb(d, v, sz);
- d->v[0] |= or;
- } while (MP_CMP(d, >=, l));
-
- /* --- Done --- */
-
- memset(v, 0, sz);
- x_free(a, v);
- return (d);
-}
-
-/*----- That's all, folks -------------------------------------------------*/