random_well512a_simd/RandomWELL512a.h

// Copyright (c) 2013, Peter Pettersson
// All rights reserved.
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#ifndef RANDOM_WELL512A_H
#define RANDOM_WELL512A_H

#include <stdlib.h>     // Needed for rand().
#include <memory.h>     // Needed for memcpy().

class RandomWELL512a
{
public:
    RandomWELL512a(int seed);
    RandomWELL512a(unsigned *seed);

    unsigned GetUnsigned();

    double GetDouble();

private:
    unsigned state[16];
    unsigned index;
};


inline RandomWELL512a::RandomWELL512a(int seed)
    : index(0)
{
    srand(seed);
    for (int i = 0; i < 16; ++i)
        state[i] = rand();
}

inline RandomWELL512a::RandomWELL512a(unsigned *seed)
    : index(0)
{
    memcpy(state, seed, 16 * sizeof(unsigned));
}

inline unsigned RandomWELL512a::GetUnsigned()
{
    #define MUTATE_LEFT(value, shift)           value ^ (value << shift)
    #define MUTATE_RIGHT(value, shift)          value ^ (value >> shift)
    #define MUTATE_LEFT_MIX(value, shift, mix)  value ^ ((value << shift) & mix)

    unsigned index_9  = (index +  9) & 15;
    unsigned index_13 = (index + 13) & 15;
    unsigned index_15 = (index + 15) & 15;

    unsigned state_index    = state[index];
    unsigned state_index_9  = state[index_9];
    unsigned state_index_13 = state[index_13];
    unsigned state_index_15 = state[index_15];

    unsigned z1	= MUTATE_LEFT(state_index, 16);
    z1 ^= MUTATE_LEFT(state_index_13, 15);

    unsigned z2	= MUTATE_RIGHT(state_index_9, 11);

    unsigned result0 = z1 ^ z2;
    state[index] = result0;

    unsigned result1 = MUTATE_LEFT(state_index_15, 2);
    result1 ^= MUTATE_LEFT(z1, 18);;
    result1 ^= z2 << 28;

    result1 ^= MUTATE_LEFT_MIX(result0, 5, 0xda442d24U);

    index = index_15;
    state[index] = result1;
    return result1;

    #undef MUTATE_LEFT
    #undef MUTATE_RIGHT
    #undef MUTATE_LEFT_MIX
}

inline double RandomWELL512a::GetDouble()
{
    const double kToFloat = 2.32830643653869628906e-10;
    return GetUnsigned() * kToFloat;
}

#endif // RANDOM_WELL512A_H