Stroop RNG test

stroop_rng.swift

import Foundation

func tally(prob: Double, precision: UInt32, maxDiff: Double, repetitions: Int) {
    var trues = 0
    let threshold = UInt32(prob * Double(precision))
    print("tally(prob: \(prob), precision: \(precision), repetitions: \(repetitions)):")
    for _ in 1...repetitions {
        let isTrue = arc4random_uniform(precision) < threshold
        if isTrue {
            trues += 1
        }
    }
    let actual = Double(trues) / Double(repetitions)
    let diff = abs(actual - prob)
    let exceeds = diff >= maxDiff
    print("- trues: \(trues) / \(repetitions) == \(actual)% diff=\(diff) \(exceeds ? "EXCEEDS!" : "ok")\n")
}

for _ in 1...10 {
    tally(prob: 0.25, precision: 100, maxDiff: 0.01, repetitions: 10_000)
    tally(prob: 0.25, precision: 1_000, maxDiff: 0.01, repetitions: 10_000)
    tally(prob: 0.25, precision: 10_000, maxDiff: 0.01, repetitions: 10_000)
}