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Libraries/MNIST/Random.swift

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+// 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)
+    }
+}