Initial commit

libsst-random/SST_SmallPRNG.c

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+/*
+	SST_SmallPRNG.c
+	Author: Chris Ertel <crertel@762studios.com>
+	Created: 2/26/2012
+
+	Purpose: 
+
+	Implementation of SmallPRNG
+
+	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"
+
+#define BIT_ROTATE(x,k) (((x)<<(k))|((x)>>(32-(k))))
+
+/*************************************************************************/
+
+typedef struct SST_SmallPRNG_Private
+{
+	uint32_t a;
+	uint32_t b;
+	uint32_t c;
+	uint32_t d;
+} SST_SmallPRNG_Private;
+
+static int sprng_random(SST_SmallPRNG_Private* x)
+{
+	uint32_t e = x->a - BIT_ROTATE(x->b, 27);
+	x->a = x->b ^ BIT_ROTATE(x->c, 17);
+	x->b = x->c + x->d;
+	x->c = x->d + e;
+	x->d = e + x->a;
+	return (int)x->d;
+}
+
+/*************************************************************************/
+
+static void SmallPRNG_InitFromSeed(void* priv, uint32_t seed)
+{
+	SST_SmallPRNG_Private* sprng = (SST_SmallPRNG_Private*)priv;
+	int i;
+	sprng->a = 0xf1ea5eed;
+	sprng->b = sprng->c = sprng->d = seed;
+	
+	for(i=0; i<20; ++i)
+		(void)sprng_random(sprng);
+}
+
+/*************************************************************************/
+
+static void SmallPRNG_GetFloatArray(void* priv, float* _out, size_t _numElements, float _min, float _max)
+{
+	SST_SmallPRNG_Private* sprng_data = (SST_SmallPRNG_Private*)priv;
+	size_t i;
+	const float diff = _max - _min;
+
+	for (i = 0; i < _numElements; i++)
+		_out[i] = _min + randIntToFloat(boundInt(sprng_random(sprng_data), 0, SST_RAND_FLOATBITS_MAX)) * diff;
+}
+
+/*************************************************************************/
+
+static int SmallPRNG_GetInt(void* priv)
+{
+	SST_SmallPRNG_Private* sprng_data = (SST_SmallPRNG_Private*)priv;
+
+	return sprng_random(sprng_data);
+}
+
+/*************************************************************************/
+
+static void SmallPRNG_GetIntArray(void* priv, int* _out, size_t _numElements, int _min, int _max)
+{
+	SST_SmallPRNG_Private* sprng_data = (SST_SmallPRNG_Private*)priv;
+	size_t i;
+
+	for (i = 0; i < _numElements; i++)
+	{
+		_out[i] = boundInt(sprng_random(sprng_data), _min, _max); /* TODO: This does redundant operations. Compilers may not be able to optimize. */
+	}
+}
+
+/*************************************************************************/
+
+/* Function table for SmallPRNG random number generator */
+const SST_PRNG_FuncTable _SST_SmallPRNGFuncTable = 
+{
+	SmallPRNG_InitFromSeed,
+	SmallPRNG_GetFloatArray,
+	SmallPRNG_GetInt,
+	SmallPRNG_GetIntArray,
+	sizeof(SST_SmallPRNG_Private)
+};