module rand // Ported from http://www.pcg-random.org/download.html // and https://github.com/imneme/pcg-c-basic/blob/master/pcg_basic.c pub struct Pcg32 { mut: state u64 inc u64 } /** * new_pcg32 - a Pcg32 PRNG generator * @param initstate - the initial state of the PRNG. * @param initseq - the stream/step of the PRNG. * @return a new Pcg32 PRNG instance */ pub fn new_pcg32(initstate u64, initseq u64) Pcg32 { mut rng := Pcg32{ } rng.state = u64(0) rng.inc = (initseq<>u64(18)) ^ oldstate)>>u64(27)) rot := u32(oldstate>>u64(59)) return ((xorshifted>>rot) | (xorshifted<<((-rot) & u32(31)))) } /** * Pcg32.bounded_next - update the PRNG state. Get the next number < bound * @param bound - the returned random number will be < bound * @return the generated pseudo random number */ [inline] pub fn (mut rng Pcg32) bounded_next(bound u32) u32 { // To avoid bias, we need to make the range of the RNG a multiple of // bound, which we do by dropping output less than a threshold. threshold := (-bound % bound) // Uniformity guarantees that loop below will terminate. In practice, it // should usually terminate quickly; on average (assuming all bounds are // equally likely), 82.25% of the time, we can expect it to require just // one iteration. In practice, bounds are typically small and only a // tiny amount of the range is eliminated. for { r := rng.next() if r >= threshold { return (r % bound) } } return u32(0) }