Merge pull request #24357 from palimondo/prng-splitmix64

[benchmark] Add SplitMix64 PRNG

Author: palimondo

benchmark/utils/TestsUtils.swift

@@ -221,6 +221,29 @@ public func Random() -> Int64 {
   return lfsrRandomGenerator.randInt()
 }
 
+// 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 &+= 0x9e3779b97f4a7c15
+        var z: UInt64 = self.state
+        z = (z ^ (z &>> 30)) &* 0xbf58476d1ce4e5b9
+        z = (z ^ (z &>> 27)) &* 0x94d049bb133111eb
+        return z ^ (z &>> 31)
+    }
+}
+
 @inlinable // FIXME(inline-always)
 @inline(__always)
 public func CheckResults(