pcg32.swift

import Cocoa

// *Really* minimal PCG32 code / (c) 2014 M.E. O'Neill / pcg-random.org
// Licensed under Apache License 2.0 (NO WARRANTY, etc. see website)
// Converted to Swift by Peter da Silva, backing out some C optimizations
// and hardcoding Knuth's LCG parameters

class pcg32_random {
    var state: UInt64;
    
    init(seed: UInt64 = 0)
    {
        state = seed
    }
    
    func next() -> UInt32
    {
        // Advance internal state, Knuth's mixed LCG
        state = state &* 6364136223846793005 &+ 1442695040888963407;
    
        // Calculate output function (XSH RR)
        let xorshifted = UInt32(truncatingBitPattern: ((state >> 18) ^ state) >> 27);
        let rot = UInt32(truncatingBitPattern: state >> 59);
        return (xorshifted >> rot) | (xorshifted << UInt32((-Int32(rot)) & 31));
    }
}

For anyone else googling for this: there are a couple of mistakes. Here is the C function it implements: https://github.com/imneme/pcg-c-basic/blob/master/pcg_basic.c#L60

Note how it ignores the inc/seq value in the algorithm, and doesn't correctly use the value of state after mutating it.

I wrote a correct version and tested it against the C library: https://gist.github.com/irskep/3a5d6cd75f4a384afff01cf742acf5be