SeededGenerator.swift

import GameKit

public class SeededGenerator: RandomNumberGenerator {
  public let seed: UInt64
  private let generator: GKMersenneTwisterRandomSource

  public convenience init() {
    self.init(seed: 0)
  }

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

  public func next() -> UInt64 {
      let a = Int32(generator.nextInt())
      let b = Int32(generator.nextInt())
      let upperBits = UInt64(UInt32(bitPattern: a)) << 32
      let lowerBits = UInt64(UInt32(bitPattern: b))
      return upperBits | lowerBits
  }
}