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

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+/* -*-c-*-
+ *
+ * Fibonacci generator
+ *
+ * (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.
+ */
+
+/*----- Notes on the Fibonacci generator ----------------------------------*
+ *
+ * The generator was originally suggested by G. J. Mitchell and D. P. Moore
+ * in 1957, and publicized by D. E. Knuth as Algorithm 3.2.2A in volume 2 of
+ * his work `The Art of Computer Programming'.  The generator is simple: at
+ * each stage it emits %$x_n = (x_{n - 55} + x_{n - 24}) \bmod 2^{32}$%.  The
+ * period is proven to be greater than %$2^{55}$%, and statistical properties
+ * appear to be good.
+ */
+
+#ifndef CATACOMB_FIBRAND_H
+#define CATACOMB_FIBRAND_H
+
+#ifdef __cplusplus
+  extern "C" {
+#endif
+
+/*----- Header files ------------------------------------------------------*/
+
+#include <mLib/bits.h>
+
+#ifndef CATACOMB_GRAND_H
+#  include "grand.h"
+#endif
+
+/*----- Magic constants ---------------------------------------------------*/
+
+#define FIB_SZ 55
+#define FIB_TAP 24
+
+/*----- Data structures ---------------------------------------------------*/
+
+typedef struct fibrand {
+  unsigned i;
+  uint32 x[FIB_SZ];
+} fibrand;
+
+/*----- Functions provided ------------------------------------------------*/
+
+/* --- @fibrand_step@ --- *
+ *
+ * Arguments:	@fibrand *f@ = pointer to Fibonacci generator context
+ *
+ * Returns:	Next output from generator.
+ *
+ * Use:		Steps the generator.  Returns
+ *		%$x_{i - 24} + x_{i - 55} \bmod 2^{32}$%.
+ */
+
+extern uint32 fibrand_step(fibrand */*f*/);
+
+/* --- @fibrand_seed@ --- *
+ *
+ * Arguments:	@fibrand *f@ = pointer to Fibonacci generator context
+ *		@grand *r@ = random number generator to extract words from
+ *
+ * Returns:	---
+ *
+ * Use:		Initializes a Fibonacci generator using word outputs from the
+ *		given random number source @r@.
+ */
+
+extern void fibrand_seed(fibrand */*f*/, grand */*r*/);
+
+/* --- @fibrand_lcseed@ --- *
+ *
+ * Arguments:	@fibrand *f@ = pointer to Fibonacci generator context
+ *		@uint32 seed@ = seed value
+ *
+ * Returns:	---
+ *
+ * Use:		Initializes a Fibonacci generator using outputs from the
+ *		@lcrand@ generator seeded from @seed@.  This is faster than
+ *		using a generic @lcrand@-based generator and @fibrand_rseed@
+ *		because it uses raw outputs rather than uniformly distributed
+ *		32-bit words.
+ */
+
+extern void fibrand_lcseed(fibrand */*f*/, uint32 /*seed*/);
+
+/* --- @fibrand_range@ --- *
+ *
+ * Arguments:	@fibrand *f@ = pointer to Fibonacci generator context
+ *		@uint32 m@ = limit
+ *
+ * Returns:	A uniformly distributed pseudorandom integer in the interval
+ *		%$[0, m)$%.
+ */
+
+extern uint32 fibrand_range(fibrand */*f*/, uint32 /*m*/);
+
+/* --- @fibrand_create@ --- *
+ *
+ * Arguments:	@uint32 seed@ = initial seed
+ *
+ * Returns:	Pointer to a generic generator.
+ *
+ * Use:		Constructs a generic generator interface over a Fibonacci
+ *		generator.  The generator is seeded using @fibrand_lcseed@.
+ */
+
+extern grand *fibrand_create(uint32 /*seed*/);
+
+/*----- That's all, folks -------------------------------------------------*/
+
+#ifdef __cplusplus
+  }
+#endif
+
+#endif