// Copyright © 2024 Apple Inc.

import Foundation

// From https://github.com/apple/swift/blob/cb0fb1ea051631219c0b944b84c78571448d58c2/benchmark/utils/TestsUtils.swift#L254
//
// This is just a seedable RandomNumberGenerator for shuffle()

// This is a fixed-increment version of Java 8's SplittableRandom generator.
// It is a very fast generator passing BigCrush, with 64 bits of state.
// See http://dx.doi.org/10.1145/2714064.2660195 and
// http://docs.oracle.com/javase/8/docs/api/java/util/SplittableRandom.html
//
// Derived from public domain C implementation by Sebastiano Vigna
// See http://xoshiro.di.unimi.it/splitmix64.c
public struct SplitMix64: RandomNumberGenerator {
    private var state: UInt64

    public init(seed: UInt64) {
        self.state = seed
    }

    public mutating func next() -> UInt64 {
        self.state &+= 0x9e37_79b9_7f4a_7c15
        var z: UInt64 = self.state
        z = (z ^ (z &>> 30)) &* 0xbf58_476d_1ce4_e5b9
        z = (z ^ (z &>> 27)) &* 0x94d0_49bb_1331_11eb
        return z ^ (z &>> 31)
    }
}