X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/ba6e6b64033b1f9de49feccb5c9cd438354481f7..0f00dc4c8eb47e67bc0f148c2dd109f73a451e0a:/rand/grand.c

diff --git a/rand/grand.c b/rand/grand.c
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+/* -*-c-*-
+ *
+ * Generic interface to random number generators
+ *
+ * (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 <stddef.h>
+
+#include <mLib/bits.h>
+
+#include "grand.h"
+
+/*----- Main code ---------------------------------------------------------*/
+
+/* --- @grand_byte@ --- *
+ *
+ * Arguments:	@grand *r@ = pointet to generic generator
+ *
+ * Returns:	A uniformly-distributed pseudorandom integer in the interval
+ *		%$[0, 256)$%.
+ */
+
+octet grand_byte(grand *r)
+{
+  if (r->ops->byte != grand_byte)
+    return (r->ops->byte(r));
+  else if (r->ops->word != grand_word)
+    return (r->ops->word(r) & 0xff);
+  else if (r->ops->fill != grand_fill) {
+    octet o;
+    r->ops->fill(r, &o, 1);
+    return (o);
+  } else
+    return (grand_range(r, 256));
+}
+
+/* --- @grand_word@ --- *
+ *
+ * Arguments:	@grand *r@ = pointet to generic generator
+ *
+ * Returns:	A uniformly-distributed pseudorandom integer in the interval
+ *		%$[0, 2^{32})$%.
+ */
+
+uint32 grand_word(grand *r)
+{
+  if (r->ops->word != grand_word)
+    return (r->ops->word(r));
+  else {
+    octet b[4];
+    grand_fill(r, b, sizeof(b));
+    return (LOAD32(b));
+  }
+}
+
+/* --- @grand_range@ --- *
+ *
+ * Arguments:	@grand *r@ = pointet to generic generator
+ *		@uint32 l@ = limit for acceptable results
+ *
+ * Returns:	A uniformly-distributed pseudorandom integer in the interval
+ *		%$[0, l)$%.
+ */
+
+uint32 grand_range(grand *r, uint32 l)
+{
+  if (r->ops->range != grand_range)
+    return (r->ops->range(r, l));
+  else {
+    uint32 m, z;
+    uint32 (*w)(grand */*r*/);
+    uint32 x;
+
+    /* --- Decide where to get data from --- *
+     *
+     * The choice of %$2^{32} - 1$% as a limit when using @grand_word@ isn't
+     * wonderful, but working with %$2^{32}$% is awkward and the loss of a
+     * few return values isn't significant.  The algorithm below still
+     * successfully returns uniformly distributed results.
+     */
+
+    if (r->ops->max) {
+      w = r->ops->raw;
+      m = r->ops->max;
+    } else {
+      w = grand_word;
+      m = 0xffffffff;
+    }
+
+    /* --- Work out maximum acceptable return value --- *
+     *
+     * This will be the highest multiple of @l@ less than @m@.
+     */
+
+    z = m - (m % l);
+
+    /* --- Generate numbers until something acceptable is found --- *
+     *
+     * This will require an expected number of attempts less than 2.
+     */
+
+    do x = w(r); while (x >= z);
+    return (x % l);
+  }
+}
+
+/* --- @grand_fill@ --- *
+ *
+ * Arguments:	@grand *r@ = pointet to generic generator
+ *		@void *p@ = pointer to a buffer
+ *		@size_t sz@ = size of the buffer
+ *
+ * Returns:	---
+ *
+ * Use:		Fills a buffer with uniformly distributed pseudorandom bytes
+ *		(see @grand_byte@).
+ */
+
+void grand_fill(grand *r, void *p, size_t sz)
+{
+  if (r->ops->fill != grand_fill)
+    r->ops->fill(r, p, sz);
+  else {
+    octet *q = p;
+    while (sz) {
+      *q++ = r->ops->byte(r);
+      sz--;
+    }
+  }
+}
+
+/*----- That's all, folks -------------------------------------------------*/