prng.c

static unsigned
wang_hash(unsigned u)
{
    u = ((u ^ 61) ^ (u >> 16)) * 9;
    u = (u ^ (u >> 4)) * 0x27d4eb2d;
    return u ^ (u >> 15);
}
static unsigned
rand_lcg(unsigned *rng)
{
    // LCG values from Numerical Recipes
    return *rng = 1664525 * (*rng) + 1013904223;;
}
static float
rand_lcg_norm(unsigned *rng)
{
    return (float)rand_lcg(rng) * (1.0f / 4294967296.0f);
}
static unsigned
rand_xorshift(unsigned *rng)
{
    // Xorshift algorithm from George Marsaglia's paper
    *rng ^= (*rng << 13);
    *rng ^= (*rng >> 17);
    *rng ^= (*rng << 5);
    return *rng;
}
static float
rand_xorshift_norm(unsigned* rng)
{
    return (float)rand_xorshift(rng) * (1.0f / 4294967296.0f);
}
static unsigned long long
hash(unsigned long long key)
{
    key = (~key) + (key << 21); // key = (key << 21) - key - 1;
    key = key ^ (key >> 24);
    key = (key + (key << 3)) + (key << 8); // key * 265
    key = key ^ (key >> 14);
    key = (key + (key << 2)) + (key << 4); // key * 21
    key = key ^ (key >> 28);
    key = key + (key << 31);
    return key;
}
static unsigned long long
hash_inv(unsigned long long key)
{
    unsigned long long tmp;
    // Invert key = key + (key << 31)
    tmp = key-(key<<31);
    key = key-(tmp<<31);

    // Invert key = key ^ (key >> 28)
    tmp = key^key>>28;
    key = key^tmp>>28;

    // Invert key *= 21
    key *= 14933078535860113213u;

    // Invert key = key ^ (key >> 14)
    tmp = key^key>>14;
    tmp = key^tmp>>14;
    tmp = key^tmp>>14;
    key = key^tmp>>14;

    // Invert key *= 265
    key *= 15244667743933553977u;

    // Invert key = key ^ (key >> 24)
    tmp = key^key>>24;
    key = key^tmp>>24;

    // Invert key = (~key) + (key << 21)
    tmp = ~key;
    tmp = ~(key-(tmp<<21));
    tmp = ~(key-(tmp<<21));
    key = ~(key-(tmp<<21));

    return key;
}
int main(int argc, char **argv)
{
    // Seed the PRNG using the thread ID and generate a few numbers...
    unsigned rng = wang_hash(threadId.x);
    unsigned r0 = rand_xorshift(&rng);
    unsigned r1 = rand_xorshift(&rng);
        
    // Generate a random float in [0, 1)...
    float f0 = rand_xorshift_norm(&rng);
    return 0;
}