1 files changed, 119 insertions, 0 deletions
diff --git a/examples/scala-js/javalib/src/main/scala/java/util/Random.scala b/examples/scala-js/javalib/src/main/scala/java/util/Random.scala
new file mode 100644
index 0000000..80428fb
--- /dev/null
+++ b/examples/scala-js/javalib/src/main/scala/java/util/Random.scala
@@ -0,0 +1,119 @@
+package java.util
+
+import scala.annotation.tailrec
+
+import scala.scalajs.js
+
+class Random(seed_in: Long) extends AnyRef with java.io.Serializable {
+
+  private var seed: Long = _
+
+  // see nextGaussian()
+  private var nextNextGaussian: Double = _
+  private var haveNextNextGaussian: Boolean = false
+
+  setSeed(seed_in)
+
+  def this() = this(Random.randomSeed())
+
+  def setSeed(seed_in: Long): Unit = {
+    seed = (seed_in ^ 0x5DEECE66DL) & ((1L << 48) - 1)
+    haveNextNextGaussian = false
+  }
+
+  protected def next(bits: Int): Int = {
+    seed = (seed * 0x5DEECE66DL + 0xBL) & ((1L << 48) - 1)
+    (seed >>> (48 - bits)).toInt
+  }
+
+  def nextDouble(): Double =
+    ((next(26).toLong << 27) + next(27)) / (1L << 53).toDouble
+
+  def nextBoolean(): Boolean = next(1) != 0
+
+  def nextInt(): Int = next(32)
+
+  def nextInt(n: Int): Int = {
+    if (n <= 0)
+      throw new IllegalArgumentException("n must be positive");
+
+    if ((n & -n) == n)  // i.e., n is a power of 2
+      ((n * next(31).toLong) >> 31).toInt
+    else {
+      @tailrec
+      def loop(): Int = {
+        val bits = next(31)
+        val value = bits % n
+        if (bits - value + (n-1) < 0) loop()
+        else value
+      }
+
+      loop()
+    }
+  }
+
+  def nextLong(): Long = (next(32).toLong << 32) + next(32)
+
+  def nextFloat(): Float = next(24) / (1 << 24).toFloat
+
+  def nextBytes(bytes: Array[Byte]): Unit = {
+    var i = 0
+    while (i < bytes.length) {
+      var rnd = nextInt()
+      var n = Math.min(bytes.length - i, 4)
+      while (n > 0) {
+        bytes(i) = rnd.toByte
+        rnd >>= 8
+        n -= 1
+        i += 1
+      }
+    }
+  }
+
+  def nextGaussian(): Double = {
+    // See http://www.protonfish.com/jslib/boxmuller.shtml
+
+    /* The Box-Muller algorithm produces two random numbers at once. We save
+     * the second one in `nextNextGaussian` to be used by the next call to
+     * nextGaussian().
+     */
+
+    if (haveNextNextGaussian) {
+      haveNextNextGaussian = false
+      return nextNextGaussian
+    }
+
+    var x, y, rds: Double = 0
+
+    /* Get two random numbers from -1 to 1.
+     * If the radius is zero or greater than 1, throw them out and pick two new
+     * ones.
+     * Rejection sampling throws away about 20% of the pairs.
+     */
+    do {
+      x = nextDouble()*2-1
+      y = nextDouble()*2-1
+      rds = x*x + y*y
+    } while (rds == 0 || rds > 1)
+
+    val c = Math.sqrt(-2 * Math.log(rds) / rds)
+
+    // Save y*c for next time
+    nextNextGaussian = y*c
+    haveNextNextGaussian = true
+
+    // And return x*c
+    x*c
+  }
+}
+
+object Random {
+
+  /** Generate a random long from JS RNG to seed a new Random */
+  private def randomSeed(): Long =
+    (randomInt().toLong << 32) | (randomInt().toLong & 0xffffffffL)
+
+  private def randomInt(): Int =
+    (Math.floor(js.Math.random() * 4294967296.0) - 2147483648.0).toInt
+
+}