A psudo random number generator that can be seeded. Use at your own

risk.


git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@4415 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/as/com/threerings/util/Random.as

@@ -0,0 +1,77 @@
+package com.threerings.util {
+
+// A simple psuedo random number generator that allows seeding.
+public class Random
+{
+    /**
+     * Creates a pseudo random number generation.
+     * 
+     * @param seed a seed of 0 will randomly seed the generator, anything
+     * other than 0 will create a generator with the specified seed.
+     */
+    public function Random (seed :uint = 0)
+    {
+        if (seed == 0) {
+            seed = uint(seedUniquifier++ + uint(Math.random() * 4294967295));
+        }
+        setSeed(seed);
+    }
+
+    /**
+     * Sets the seed of the generator.  This will result in the same generator
+     * sequence of values as a new generator created with the specified seed.
+     */
+    public function setSeed (seed :uint) :void
+    {
+        seed = uint(seed ^ multiplier);
+    }
+
+    /**
+     * Returns the an int value n where 0 <= value < n.
+     *
+     * @param n the range to return.  If this is set to 0 it will return a
+     * random integer value.  Anything less than 0 will thrown an error.
+     */
+    public function nextInt (n :int=0) :int
+    {
+        if (n < 0)
+            throw new Error("n must be positive");
+
+        if (n == 0) return int(next(32));
+
+        var bits :int, val :int;
+        do {
+            bits = int(next(31));
+            val = bits % n;
+        } while (bits - val + (n - 1) < 0);
+        return val;
+    }
+
+    /**
+     * Returns a random Boolean value.
+     */
+    public function nextBoolean () :Boolean
+    {
+        return next(1) != 0;
+    }
+
+    /**
+     * Returns a random Number where 0.0 <= value < 1.0.
+     */
+    public function nextNumber () :Number
+    {
+        return Number(next(32) / (1 << 32));
+    }
+
+    protected function next (bits :int) :uint
+    {
+        seed = uint(seed * multiplier + addend)
+        return uint(seed >>> (32 - bits));
+    }
+
+    protected var seed :uint;
+    protected static var seedUniquifier :uint = 2812526361;
+    protected static const multiplier :uint = 452871439;
+    protected static const addend :uint = 11;
+}
+}