replace darwin prng with higher quality prngs

Sources/Voxelotl/Random/PCG32Random.swift

@@ -0,0 +1,47 @@
+public struct PCG32Random: RandomProvider {
+  public typealias Output = UInt32
+
+  public static var min: UInt32 { .min }
+  public static var max: UInt32 { .max }
+
+  private var _state: UInt64, _inc: UInt64
+
+  public var state: (UInt64, UInt64) {
+    get { (self._state, self._inc) }
+    set {
+      self._state = newValue.0
+      self._inc   = newValue.1
+    }
+  }
+
+  init() {
+    self._state = 0x853C49E6748FEA9B
+    self._inc   = 0xDA3E39CB94B95BDB
+  }
+
+  public init(seed: UInt64, sequence: UInt64) {
+    self.init()
+    self.seed(state: _state, sequence: sequence)
+  }
+
+  public mutating func seed(state: UInt64, sequence: UInt64) {
+    self._state = 0
+    self._inc   = sequence << 1 | 0x1
+    _ = next()
+    self._state &+= state
+    _ = next()
+  }
+
+  public mutating func next() -> UInt32 {
+    let prevState = self._state
+
+    // LCG component
+    self._state &*= 6364136223846793005
+    self._state &+= self._inc
+
+    // Permutation (XorShift + RotRight)
+    let xorShifted = UInt32(truncatingIfNeeded: (prevState &>> 18 ^ prevState) &>> 27)
+    let rot59 = UInt32(truncatingIfNeeded: prevState &>> 59)
+    return xorShifted &>> rot59 | xorShifted &<< UInt32(bitPattern: -Int32(bitPattern: rot59) & 0x1F)
+  }
+}