XORShift.swift

import Foundation

// XORShiftのRandomNumberGenerator
// 参考: https://ja.wikipedia.org/wiki/Xorshift

struct XORShift: RandomNumberGenerator {
    private var y: UInt64

    init(seed: UInt64 = 2463534242) {
        y = seed > 0 ? seed : 2463534242
        next()
    }

    mutating func next() -> UInt64 {
        y = y ^ (y << 13)
        y = y ^ (y >> 17)
        y = y ^ (y << 5)
        return y
    }
}

struct XORShift64: RandomNumberGenerator {
    private var x: UInt64

    init(seed: UInt64 = 88172645463325252) {
        x = seed > 0 ? seed : 88172645463325252
        next()
    }

    mutating func next() -> UInt64 {
        x = x ^ (x << 13)
        x = x ^ (x >> 7)
        x = x ^ (x << 17)
        return x
    }
}

struct XORShift96: RandomNumberGenerator {
    private var x: UInt64
    private var y: UInt64 = 362436069
    private var z: UInt64 = 521288629

    init(seed: UInt64 = 123456789) {
        x = seed > 0 ? seed : 123456789
        next()
    }

    mutating func next() -> UInt64 {
        let t = (x ^ (x << 3)) ^ (y ^ (y >> 19)) ^ (z ^ (z << 6))
        x = y
        y = z
        z = t
        return z
    }
}

struct XORShift128: RandomNumberGenerator {
    private var x: UInt64
    private var y: UInt64 = 362436069
    private var z: UInt64 = 521288629
    private var w: UInt64 = 88675123

    init(seed: UInt64 = 123456789) {
        x = seed > 0 ? seed : 123456789
        next()
    }

    mutating func next() -> UInt64 {
        let t = x ^ (x << 11)
        x = y
        y = z
        z = w
        w = (w ^ (w >> 19)) ^ (t ^ (t >> 8))
        return w
    }
}

// テスト

var stack: [Bool] = []
//var xor = XORShift(seed: UInt64(Date().timeIntervalSince1970))
var xor = XORShift(seed: 111111111111111111)
(0..<100).forEach { _ in
    if Int.random(in: 0..<10000, using: &xor) < 1000 {
        stack.append(true)
    } else {
        stack.append(false)
    }
}
print(stack.map { "\($0)" }.joined(separator: ", "))
let counter = NSCountedSet(array: stack)
print("t: \(counter.count(for: true)), f: \(counter.count(for: false))")