ab_rand.h

// Derived from
// http://burtleburtle.net/bob/rand/smallprng.html
// TODO(alex): SSE intrinsic
#if !defined(AB_RAND_H)
#define AB_RAND_H
#define ULONG_MAXF 4294967295.0 // 2^32-1

// Internal affixation, _
// 32 bit (u4, ulong)
#define _ab_rand_rot(x,k) (((x)<<(k))|((x)>>(32-(k))))
typedef unsigned long int u4;
typedef struct ab_random_series { u4 a; u4 b; u4 c; u4 d; } ab_random_series;

// [0, ULONG_MAXF]
u4 ab_random(ab_random_series *Series) {
    u4 e = Series->a - _ab_rand_rot(Series->b, 27);
    Series->a = Series->b ^ _ab_rand_rot(Series->b, 17);
    Series->b = Series->c + Series->d;
    Series->c = Series->d + e;
    Series->d = e + Series->a;
    return Series->d;
}
// [0, 1]
float ab_random_unilateral(ab_random_series *Series) {
    float Result = ab_random(Series) / ULONG_MAXF;
    return(Result);
}
// [-1, 1]
float ab_random_bilateral(ab_random_series *Series) {
    float Result = ab_random_unilateral(Series) * 2.0 - 1.0;
    return(Result);
}
// [Min, Max]
u4 ab_random_between(ab_random_series *Series, u4 Min, u4 Max) {
    u4 Result = ab_random(Series) % (Max - Min) + Min;
    return Result;
}
void ab_random_seed(ab_random_series *Series, u4 Seed) {
    Series->a = 0xf1ea5eed, Series->b = Series->c = Series->d = Seed;
    for (int SeedIndex = 0; SeedIndex < 20; ++SeedIndex) {
        (void)ab_random(Series);
    }
}
#endif