101 lines
2.6 KiB
C
101 lines
2.6 KiB
C
/*
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SST_SmallPRNG.c
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Author: Chris Ertel <crertel@762studios.com>
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Created: 2/26/2012
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Purpose:
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Implementation of SmallPRNG
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License:
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This program is free software. It comes without any warranty, to
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the extent permitted by applicable law. You can redistribute it
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and/or modify it under the terms of the Do What The Fuck You Want
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To Public License, Version 2, as published by Sam Hocevar. See
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http://sam.zoy.org/wtfpl/COPYING for more details.
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*/
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#include "RandomFuncTbl.h"
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#define BIT_ROTATE(x,k) (((x)<<(k))|((x)>>(32-(k))))
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/*************************************************************************/
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typedef struct SST_SmallPRNG_Private
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{
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uint32_t a;
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uint32_t b;
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uint32_t c;
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uint32_t d;
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} SST_SmallPRNG_Private;
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static int sprng_random(SST_SmallPRNG_Private* x)
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{
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uint32_t e = x->a - BIT_ROTATE(x->b, 27);
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x->a = x->b ^ BIT_ROTATE(x->c, 17);
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x->b = x->c + x->d;
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x->c = x->d + e;
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x->d = e + x->a;
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return (int)x->d;
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}
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/*************************************************************************/
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static void SmallPRNG_InitFromSeed(void* priv, uint32_t seed)
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{
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SST_SmallPRNG_Private* sprng = (SST_SmallPRNG_Private*)priv;
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int i;
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sprng->a = 0xf1ea5eed;
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sprng->b = sprng->c = sprng->d = seed;
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for(i=0; i<20; ++i)
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(void)sprng_random(sprng);
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}
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/*************************************************************************/
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static void SmallPRNG_GetFloatArray(void* priv, float* _out, size_t _numElements, float _min, float _max)
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{
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SST_SmallPRNG_Private* sprng_data = (SST_SmallPRNG_Private*)priv;
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size_t i;
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const float diff = _max - _min;
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for (i = 0; i < _numElements; i++)
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_out[i] = _min + randIntToFloat(boundInt(sprng_random(sprng_data), 0, SST_RAND_FLOATBITS_MAX)) * diff;
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}
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/*************************************************************************/
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static int SmallPRNG_GetInt(void* priv)
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{
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SST_SmallPRNG_Private* sprng_data = (SST_SmallPRNG_Private*)priv;
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return sprng_random(sprng_data);
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}
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/*************************************************************************/
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static void SmallPRNG_GetIntArray(void* priv, int* _out, size_t _numElements, int _min, int _max)
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{
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SST_SmallPRNG_Private* sprng_data = (SST_SmallPRNG_Private*)priv;
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size_t i;
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for (i = 0; i < _numElements; i++)
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{
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_out[i] = boundInt(sprng_random(sprng_data), _min, _max); /* TODO: This does redundant operations. Compilers may not be able to optimize. */
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}
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}
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/*************************************************************************/
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/* Function table for SmallPRNG random number generator */
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const SST_PRNG_FuncTable _SST_SmallPRNGFuncTable =
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{
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SmallPRNG_InitFromSeed,
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SmallPRNG_GetFloatArray,
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SmallPRNG_GetInt,
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SmallPRNG_GetIntArray,
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sizeof(SST_SmallPRNG_Private)
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};
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