Add random number generator and related functions

src/rng.c

@@ -0,0 +1,128 @@
+/*
+ * Copyright (C) 2010 Julien BLACHE <jb@jblache.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <errno.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/types.h>
+#include <stdint.h>
+
+#include <gcrypt.h>
+
+#include "rng.h"
+
+
+/* Park & Miller Minimal Standard PRNG
+ * w/ Bays-Durham shuffle
+ * From Numerical Recipes in C, 2nd ed.
+ */
+static int32_t
+rng_rand_internal(int32_t *seed)
+{
+  int32_t hi;
+  int32_t lo;
+  int32_t res;
+
+  hi = *seed / 127773;
+  lo = *seed % 127773;
+
+  res = 16807 * lo - 2836 * hi;
+
+  if (res < 0)
+    res += 0x7fffffffL; /* 2147483647 */
+
+  *seed = res;
+
+  return res;
+}
+
+void
+rng_init(struct rng_ctx *ctx)
+{
+  int32_t val;
+  int i;
+
+  gcry_randomize(&ctx->seed, sizeof(ctx->seed), GCRY_STRONG_RANDOM);
+
+  /* Load the shuffle array - first 8 iterations discarded */
+  for (i = sizeof(ctx->iv) / sizeof(ctx->iv[0]) + 7; i >= 0; i--)
+    {
+      val = rng_rand_internal(&ctx->seed);
+
+      if (i < sizeof(ctx->iv) / sizeof(ctx->iv[0]))
+	ctx->iv[i] = val;
+    }
+
+  ctx->iy = ctx->iv[0];
+}
+
+int32_t
+rng_rand(struct rng_ctx *ctx)
+{
+  int i;
+
+  /* Select return value */
+  i = ctx->iy / (1 + (0x7fffffffL - 1) / (sizeof(ctx->iv) / sizeof(ctx->iv[0])));
+  ctx->iy = ctx->iv[i];
+
+  /* Refill */
+  ctx->iv[i] = rng_rand_internal(&ctx->seed);
+
+  return ctx->iy;
+}
+
+/* Integer in [min, max[, min >= 0 */
+int32_t
+rng_rand_range(struct rng_ctx *ctx, int32_t min, int32_t max)
+{
+  int32_t res;
+  int32_t range;
+
+  range = max - min;
+
+  res = rng_rand(ctx);
+  res = (int32_t)((double)range * ((1.0 / 2147483647.0) * (double)res));
+
+  if (min > 0)
+    res += min;
+
+  return res;
+}
+
+/* Fisher-Yates shuffling algorithm
+ * Durstenfeld in-place shuffling variant
+ */
+void
+shuffle_ptr(struct rng_ctx *ctx, void **values, int len)
+{
+  int i;
+  int32_t j;
+  void *tmp;
+
+  for (i = len - 1; i > 0; i--)
+    {
+      j = rng_rand_range(ctx, 0, i + 1);
+
+      tmp = values[i];
+      values[i] = values[j];
+      values[j] = tmp;
+    }
+}
+

src/rng.h

@@ -0,0 +1,25 @@
+
+#ifndef __RNG_H__
+#define __RNG_H__
+
+struct rng_ctx {
+  int32_t iy;
+  int32_t iv[32]; /* shuffle array */
+  int32_t seed;
+};
+
+
+void
+rng_init(struct rng_ctx *ctx);
+
+int32_t
+rng_rand(struct rng_ctx *ctx);
+
+int32_t
+rng_rand_range(struct rng_ctx *ctx, int32_t min, int32_t max);
+
+void
+shuffle_ptr(struct rng_ctx *ctx, void **values, int len);
+
+#endif /* !__RNG_H__ */
+