split split mix sixty four

Sources/Voxelotl/CMakeLists.txt

@@ -28,6 +28,7 @@ add_executable(Voxelotl MACOSX_BUNDLE
   Random/PerlinNoiseGenerator.swift
   Random/SimplexNoise.swift
   Random/RandomCollectionExtensions.swift
+  Random/SplitMix64.swift
 
   # Resource classes
   NSImageLoader.swift

Sources/Voxelotl/Random/PCG32Random.swift

@@ -1,5 +1,6 @@
-public struct PCG32Random: RandomProvider, RandomStateAccess {
+public struct PCG32Random: RandomProvider, RandomSeedable, RandomStateAccess {
   public typealias Output = UInt32
+  public typealias SeedType = (UInt64, UInt64)
   public typealias StateType = (UInt64, UInt64)
 
   public static var min: UInt32 { .min }
@@ -21,11 +22,20 @@ public struct PCG32Random: RandomProvider, RandomStateAccess {
   }
 
   public init(state: (UInt64, UInt64)) {
-    self.init()
+    self._state = state.0
-    self.reset(state: state.0, sequence: state.1)
+    self._inc   = state.1
   }
 
-  public mutating func reset(state: UInt64, sequence: UInt64) {
+  public init(seed: (UInt64, UInt64)) {
+    self.init()
+    self.seed(state: seed.0, sequence: seed.1)
+  }
+
+  public mutating func seed(_ seed: (UInt64, UInt64)) {
+    self.seed(state: seed.0, sequence: seed.1)
+  }
+
+  public mutating func seed(state: UInt64, sequence: UInt64) {
     self._state = 0
     self._inc   = sequence << 1 | 0x1
     _ = next()

Sources/Voxelotl/Random/RandomProvider.swift

@@ -8,7 +8,7 @@ public protocol RandomProvider {
 }
 
 public protocol RandomSeedable {
-  associatedtype SeedType: FixedWidthInteger
+  associatedtype SeedType
 
   init(seed: SeedType)
   mutating func seed(_ value: SeedType)

Sources/Voxelotl/Random/SplitMix64.swift

@@ -0,0 +1,25 @@
+public struct SplitMix64: RandomProvider, RandomSeedable {
+  public typealias Output = UInt64
+  public typealias SeedType = UInt64
+
+  public static var min: UInt64 { .max }
+  public static var max: UInt64 { .min }
+
+  private var _state: UInt64
+
+  public init(seed: UInt64) {
+    self._state = seed
+  }
+
+  public mutating func seed(_ value: UInt64) {
+    self._state = value
+  }
+
+  public mutating func next() -> UInt64 {
+    var x = self._state &+ 0x9E3779B97F4A7C15
+    x = (x ^ x &>> 30) &* 0xBF58476D1CE4E5B9
+    x = (x ^ x &>> 27) &* 0x94D049BB133111EB
+    self._state = x ^ x &>> 31
+    return self._state
+  }
+}

Sources/Voxelotl/Random/Xoroshiro128.swift

@@ -1,10 +1,9 @@
-struct Xoroshiro128Plus: RandomProvider, RandomSeedable, RandomStateAccess {
+public struct Xoroshiro128Plus: RandomProvider, RandomStateAccess {
   public typealias Output = UInt64
-  public typealias SeedType = UInt64
   public typealias StateType = (UInt64, UInt64)
 
-  static public var min: UInt64 { .min }
+  public static var min: UInt64 { .min }
-  static public var max: UInt64 { .max }
+  public static var max: UInt64 { .max }
 
   public var state: (UInt64, UInt64)
 
@@ -16,16 +15,6 @@ struct Xoroshiro128Plus: RandomProvider, RandomSeedable, RandomStateAccess {
     self.state = (state.0, state.1)
   }
 
-  public init(seed: UInt64) {
-    let s0 = splitMix64(seed: seed)
-    self.init(state: (s0, splitMix64(seed: s0)))
-  }
-
-  public mutating func seed(_ seed: UInt64) {
-    let s0 = splitMix64(seed: seed)
-    self.state = (s0, splitMix64(seed: s0))
-  }
-
   public mutating func next() -> UInt64 {
     let result = self.state.0 &+ self.state.1
 
@@ -38,13 +27,12 @@ struct Xoroshiro128Plus: RandomProvider, RandomSeedable, RandomStateAccess {
   }
 }
 
-struct Xoroshiro128PlusPlus: RandomProvider, RandomSeedable, RandomStateAccess {
+public struct Xoroshiro128PlusPlus: RandomProvider, RandomStateAccess {
   public typealias Output = UInt64
-  public typealias SeedType = UInt64
   public typealias StateType = (UInt64, UInt64)
 
-  static public var min: UInt64 { .min }
+  public static var min: UInt64 { .min }
-  static public var max: UInt64 { .max }
+  public static var max: UInt64 { .max }
 
   public var state: (UInt64, UInt64)
 
@@ -56,16 +44,6 @@ struct Xoroshiro128PlusPlus: RandomProvider, RandomSeedable, RandomStateAccess {
     self.state = (state.0, state.1)
   }
 
-  public init(seed: UInt64) {
-    let s0 = splitMix64(seed: seed)
-    self.init(state: (s0, splitMix64(seed: s0)))
-  }
-
-  public mutating func seed(_ seed: UInt64) {
-    let s0 = splitMix64(seed: seed)
-    self.state = (s0, splitMix64(seed: s0))
-  }
-
   public mutating func next() -> UInt64 {
     let result = (self.state.0 &+ self.state.1).rotate(left: 17) &+ self.state.0
 
@@ -78,13 +56,12 @@ struct Xoroshiro128PlusPlus: RandomProvider, RandomSeedable, RandomStateAccess {
   }
 }
 
-struct Xoroshiro128StarStar: RandomProvider, RandomSeedable, RandomStateAccess {
+public struct Xoroshiro128StarStar: RandomProvider, RandomStateAccess {
   public typealias Output = UInt64
-  public typealias SeedType = UInt64
   public typealias StateType = (UInt64, UInt64)
 
-  static public var min: UInt64 { .min }
+  public static var min: UInt64 { .min }
-  static public var max: UInt64 { .max }
+  public static var max: UInt64 { .max }
 
   public var state: (UInt64, UInt64)
 
@@ -96,16 +73,6 @@ struct Xoroshiro128StarStar: RandomProvider, RandomSeedable, RandomStateAccess {
     self.state = (state.0, state.1)
   }
 
-  public init(seed: UInt64) {
-    let s0 = splitMix64(seed: seed)
-    self.init(state: (s0, splitMix64(seed: s0)))
-  }
-
-  public mutating func seed(_ seed: UInt64) {
-    let s0 = splitMix64(seed: seed)
-    self.state = (s0, splitMix64(seed: s0))
-  }
-
   public mutating func next() -> UInt64 {
     let result = (self.state.0 &* 5).rotate(left: 7) &* 9
 
@@ -119,14 +86,7 @@ struct Xoroshiro128StarStar: RandomProvider, RandomSeedable, RandomStateAccess {
 }
 
 fileprivate extension UInt64 {
-  func rotate(left count: Int) -> Self {
+  @inline(__always) func rotate(left count: Int) -> Self {
     self &<< count | self &>> (Self.bitWidth &- count)
   }
 }
-
-fileprivate func splitMix64(seed: UInt64) -> UInt64 {
-  var x = seed &+ 0x9E3779B97F4A7C15
-  x = (x ^ x &>> 30) &* 0xBF58476D1CE4E5B9
-  x = (x ^ x &>> 27) &* 0x94D049BB133111EB
-  return x ^ x &>> 31
-}

Sources/Voxelotl/WorldGenerator.swift

@@ -3,13 +3,11 @@ struct WorldGenerator {
 
   public mutating func reset(seed: UInt64) {
     var random: any RandomProvider
+    let initialState = SplitMix64.createState(seed: seed)
 #if true
-    random = Xoroshiro128PlusPlus(seed: seed)
+    random = Xoroshiro128PlusPlus(state: initialState)
 #else
-    //TODO: Fill seed with a hash
+    random = PCG32Random(seed: initialState)
-    random = PCG32Random(state: (
-      UInt64(Arc4Random.instance.next()) | UInt64(Arc4Random.instance.next()) << 32,
-      UInt64(Arc4Random.instance.next()) | UInt64(Arc4Random.instance.next()) << 32))
 #endif
 
     self.noise = ImprovedPerlin<Float>(random: &random)
@@ -38,3 +36,11 @@ struct WorldGenerator {
     return chunk
   }
 }
+
+fileprivate extension RandomProvider where Output == UInt64, Self: RandomSeedable, SeedType == UInt64 {
+  static func createState(seed value: UInt64) -> (UInt64, UInt64) {
+    var hash = Self(seed: value)
+    let state = (hash.next(), hash.next())
+    return state
+  }
+}