--- /dev/null
+/* -*-c-*-
+ *
+ * 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 -------------------------------------------------*/