use arc4random to seed non-csprng, fleshes out random subsystem

Sources/Voxelotl/Random/Arc4Random.swift

@@ -17,8 +17,12 @@ public class Arc4Random: RandomProvider {
     arc4random()
   }
 
-  public func next(in bound: Range<Int>) -> Int {
-    assert(bound.upperBound <= Self.max)
-    return bound.lowerBound + Int(arc4random_uniform(UInt32(bound.upperBound)))
+  public func next(in bound: Int) -> Int {
+    assert(bound <= Self.max)
+    return Int(arc4random_uniform(UInt32(bound)))
+  }
+
+  public func next(in range: Range<Int>) -> Int {
+    return range.lowerBound + next(in: range.upperBound - range.lowerBound)
   }
 }

Sources/Voxelotl/Random/DarwinRandom.swift

@@ -0,0 +1,33 @@
+public struct DarwinRandom: RandomProvider {
+  public typealias Output = Int
+
+  public static var min: Int { 0x00000000 }
+  public static var max: Int { 0x7FFFFFFF }
+
+  private var state: Int
+
+  init() {
+    self.state = 0
+  }
+
+  public init(seed: Int) {
+    self.state = seed
+  }
+
+  mutating public func seed(with seed: Int) {
+    self.state = seed
+  }
+
+  mutating public func next() -> Int {
+    if self.state == 0 {
+      self.state = 123459876
+    }
+    let hi = self.state / 127773
+    let lo = self.state - hi * 127773
+    self.state = 16807 * lo - 2836 * hi
+    if self.state < 0 {
+      self.state += Self.max
+    }
+    return self.state % (Self.max + 1)
+  }
+}

Sources/Voxelotl/Random/RandomRange.swift

@@ -0,0 +1,20 @@
+public extension RandomProvider where Output: BinaryInteger {
+  mutating func next(in range: Range<Int>) -> Int {
+    range.lowerBound + self.next(in: range.upperBound - range.lowerBound)
+  }
+
+  mutating func next(in range: ClosedRange<Int>) -> Int {
+    range.lowerBound + self.next(in: range.upperBound - range.lowerBound + 1)
+  }
+
+  mutating func next(in bound: Int) -> Int {
+    assert(Self.min == 0)
+    assert(Self.max >= bound)
+    let threshold = Int(Self.max % Output(bound))
+    var result: Int
+    repeat {
+      result = Int(truncatingIfNeeded: self.next())
+    } while result < threshold
+    return result % bound
+  }
+}