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libsst-random/SST_Mersenne.c

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+/*
+	SST_Mersenne.c
+	Author: Chris Ertel <crertel@762studios.com>
+	Created: 2/26/2012
+
+	Purpose: 
+
+	Implementation of Mersenne Twister
+
+	License:
+
+	This program is free software. It comes without any warranty, to
+	the extent permitted by applicable law. You can redistribute it
+	and/or modify it under the terms of the Do What The Fuck You Want
+	To Public License, Version 2, as published by Sam Hocevar. See
+	http://sam.zoy.org/wtfpl/COPYING for more details.
+*/
+
+#include "RandomFuncTbl.h"
+
+/*
+Note: This implementation of mersenne twister was originally written by Michael Brundage and has 
+been placed in the public domain.  We modified it somewhat.
+*/
+
+/* Length of our mersenne twister buffer */
+#define MT_LEN 624
+
+/* Bunch of useful macro functions and magic numbers */
+#define MT_IA           397
+#define MT_IB           (MT_LEN - MT_IA)
+#define UPPER_MASK      0x80000000
+#define LOWER_MASK      0x7FFFFFFF
+#define MATRIX_A        0x9908B0DF
+#define SEED_MAGIC		0x6C078965
+#define TWIST(b,i,j)    ((b)[i] & UPPER_MASK) | ((b)[j] & LOWER_MASK)
+#define MAGIC(s)        (((s)&1)*MATRIX_A)
+
+/*************************************************************************/
+
+/* Mersenne Twister Data Struct */
+typedef struct SST_Mersenne_Private
+{
+	uint32_t mt_buffer[MT_LEN];	/* Buffer for our seed data */
+	size_t mt_index;
+} SST_Mersenne_Private;
+
+/*************************************************************************/
+
+/* get the next random value from the mersenne twister array */
+static int mt_random(SST_Mersenne_Private* mt)
+{
+	uint32_t* b = mt->mt_buffer;
+	size_t idx = mt->mt_index;
+
+	uint32_t s;
+	int i;
+
+	if(idx == MT_LEN)
+	{
+		idx = 0;
+		i = 0;
+		for (; i < MT_IB; i++) {
+			s = TWIST(b, i, i+1);
+			b[i] = b[i + MT_IA] ^ (s >> 1) ^ MAGIC(s);
+		}
+		for (; i < MT_LEN-1; i++) {
+			s = TWIST(b, i, i+1);
+			b[i] = b[i - MT_IB] ^ (s >> 1) ^ MAGIC(s);
+		}
+
+		s = TWIST(b, MT_LEN-1, 0);
+		b[MT_LEN-1] = b[MT_IA-1] ^ (s >> 1) ^ MAGIC(s);
+	}
+
+	mt->mt_index = idx + 1;
+
+	return (int)b[idx];
+}
+
+/*************************************************************************/
+
+static void Mersenne_InitFromSeed(void* priv, uint32_t seed)
+{
+	SST_Mersenne_Private* mt_data = (SST_Mersenne_Private*)priv;
+	size_t i;
+
+	mt_data->mt_index = 0;
+	mt_data->mt_buffer[0] = seed;
+
+	/* Initialize the generator */
+	for(i = 1; i < MT_LEN; i++)
+		mt_data->mt_buffer[i] = (SEED_MAGIC * (mt_data->mt_buffer[i - 1] ^ (mt_data->mt_buffer[i - 1] >> 30)) + (uint32_t)i);
+
+}
+
+/*************************************************************************/
+
+static void Mersenne_GetFloatArray(void* priv, float* _out, size_t _numElements, float _min, float _max)
+{
+	SST_Mersenne_Private* mt_data = (SST_Mersenne_Private*)priv;
+	size_t i;
+	const float diff = _max - _min;
+	
+	/* grab a number of pseudorandom floating point numbers in the specified range */
+	for (i = 0; i < _numElements; i++)
+	{
+		_out[i] = _min + randIntToFloat((uint32_t)boundInt(mt_random(mt_data), 0, SST_RAND_FLOATBITS_MAX)) * diff; /* x = [0,1];  value = min + x*(max - min) */
+	}
+}
+
+/*************************************************************************/
+
+static int Mersenne_GetInt(void* priv)
+{
+	SST_Mersenne_Private* mt_data = (SST_Mersenne_Private*)priv;
+	
+	return mt_random(mt_data);
+}
+
+/*************************************************************************/
+
+static void Mersenne_GetIntArray(void* priv, int* _out, size_t _numElements, int _min, int _max)
+{
+	SST_Mersenne_Private* mt_data = (SST_Mersenne_Private*)priv;
+	size_t i;
+
+	/* grab an number of pseudorandom ints in the specified range */
+	for (i = 0; i <_numElements; i++)
+		_out[i] = boundInt(mt_random(mt_data), _min, _max);
+}
+
+/*************************************************************************/
+
+/* Function table for mersenne random number generation. */
+const SST_PRNG_FuncTable _SST_MersenneFuncTable = 
+{
+	Mersenne_InitFromSeed,
+	Mersenne_GetFloatArray,
+	Mersenne_GetInt,
+	Mersenne_GetIntArray,
+	sizeof(SST_Mersenne_Private)
+};