60 lines
1.4 KiB
Swift
60 lines
1.4 KiB
Swift
import Foundation
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public enum Xoshiro256: Equatable {
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public typealias State = (UInt64, UInt64, UInt64, UInt64)
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internal static var invalidState: State { (0, 0, 0, 0) }
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internal static func isValid(state: State) -> Bool {
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state != invalidState
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}
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}
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@inlinable
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@inline(__always)
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internal func rotl(_ x: UInt64, _ k: UInt64) -> UInt64 {
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(x << k) | (x >> (64 &- k))
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}
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struct Xoshiro256Plus: RandomNumberGenerator {
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public typealias State = Xoshiro256.State
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private var state: State
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public init() {
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var generator = SystemRandomNumberGenerator()
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self.init(seed: generator.next())
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}
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public init(seed: UInt64) {
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var generator = SplitMix64(state: seed)
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var state = Xoshiro256.invalidState
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repeat {
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state = (generator.next(), generator.next(), generator.next(), generator.next())
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} while !Xoshiro256.isValid(state: state)
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self.init(state: state)
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}
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public init(state: State) {
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precondition(Xoshiro256.isValid(state: state), "The state must not be zero")
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self.state = state
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}
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public mutating func next() -> UInt64 {
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let result = state.0 &+ state.3
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let t = state.1 << 17
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state.2 ^= state.0
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state.3 ^= state.1
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state.1 ^= state.2
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state.0 ^= state.3
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state.2 ^= t
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state.3 = rotl(state.3, 45)
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return result
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}
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}
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