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apple/PhysarumApp/Tests/TestSupport.swift

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import Foundation

/// Deterministic SplitMix64 RNG so randomize/mutate tests are reproducible.
struct SeededGenerator: RandomNumberGenerator {
    private var state: UInt64
    init(seed: UInt64) { state = seed }
    mutating func next() -> UInt64 {
        state = state &+ 0x9E37_79B9_7F4A_7C15
        var z = state
        z = (z ^ (z >> 30)) &* 0xBF58_476D_1CE4_E5B9
        z = (z ^ (z >> 27)) &* 0x94D0_49BB_1331_11EB
        return z ^ (z >> 31)
    }
}