UT_FastRandom.h

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/*
 * PROPRIETARY INFORMATION.  This software is proprietary to
 * Side Effects Software Inc., and is not to be reproduced,
 * transmitted, or disclosed in any way without written permission.
 *
 * NAME: UT_FastRandom ( UT Library, C++)
 *
 * COMMENTS:
 *   An implementation of George Marsaglia's XOR-128 random number
 *   generator. This generator has a period of 2^128-1, is extremely fast, and
 *   unlike the Mersenne Twister, has negligible seeding time.
 *   http://www.jstatsoft.org/v08/i14/paper
 */

#ifndef __UT_FastRandom__
#define __UT_FastRandom__

#include "UT_API.h"
#include <SYS/SYS_Types.h>
#include <stdint.h>

class UT_API UT_FastRandom
{
public:
                UT_FastRandom()
                {
                    setSeed(0);
                }
                
    void        setSeed(uint seed)
                {
                    mySeeds[0] = seed ^ 123456789U;
                    for (int i = 1; i < 4; i++)
                    {
                        // See Knuth TAOCP Vol 12. P. 106 for multiplier
                        mySeeds[i] = 1812433253U *
                                     (mySeeds[i-1] ^ (mySeeds[i-1] >> 30)) + i;
                    }
                }

    /// Returns a random 32-bit unsigned integer.
    uint        urandom()
                {
                    // Note: The shift constants are very carefully selected,
                    // so don't change them arbitrarily.
                    uint                t;
                    t = mySeeds[0] ^ (mySeeds[0] << 11);
                    mySeeds[0] = mySeeds[1];
                    mySeeds[1] = mySeeds[2];
                    mySeeds[2] = mySeeds[3];
                    mySeeds[3] = (mySeeds[3] ^ (mySeeds[3] >> 19)) ^
                                 (t ^ (t >> 8));
                    return mySeeds[3];
                }

    /// Returns a random float between [0,1).
    float       frandom()
                {
                    SYS_FPRealUnionF    tmp;
                    tmp.uval = 0x3f800000 | (0x007fffff & urandom());
                    return tmp.fval - CONST_FPREAL32(1.0);
                }
                
private:
    uint        mySeeds[4];
};

/// Fast random number generator.
/// Reference: https://software.intel.com/en-us/articles/fast-random-number-generator-on-the-intel-pentiumr-4-processor
inline int UTfastRand(uint &seed)
{
    seed = (214013*seed+2531011);

    return (seed>>16)&0x7FFF;
}

/// Fast random number generator. Float variant, with values in [0,1).
inline float UTfastRandF(uint &seed)
{
    return float(UTfastRand(seed)) / (INT16_MAX-1);
}

#endif // __UT_FastRandom__