From 4d8d0f37887e42b9db7fd772ffe59fb034e24b2c Mon Sep 17 00:00:00 2001
From: ray <ray@6335cc39-0255-0410-8fd6-9bcaacd3b74c>
Date: Fri, 29 Jun 2007 00:32:12 +0000
Subject: [PATCH] From Charlie Groves: - Added a version of getWeightedIndex()
 that takes a float[] the Random to use for picking.

git-svn-id: https://samskivert.googlecode.com/svn/trunk@2119 6335cc39-0255-0410-8fd6-9bcaacd3b74c
---
 src/java/com/samskivert/util/RandomUtil.java | 35 ++++++++++++++++++--
 1 file changed, 33 insertions(+), 2 deletions(-)

diff --git a/src/java/com/samskivert/util/RandomUtil.java b/src/java/com/samskivert/util/RandomUtil.java
index 4ca99698..9765b809 100644
--- a/src/java/com/samskivert/util/RandomUtil.java
+++ b/src/java/com/samskivert/util/RandomUtil.java
@@ -69,9 +69,21 @@ public class RandomUtil
      */
     public static float getFloat (float high)
     {
-        return rand.nextFloat() * high;
+        return getFloat(high, rand);
     }
 
+    /**
+     * Returns a pseudorandom, uniformly distributed float value between
+     * 0.0 (inclusive) and the specified value (exclusive).
+     *
+     * @param high the high value limiting the random number sought.
+     * @param r the random number generator to use
+     */
+    public static float getFloat (float high, Random r)
+    {
+         return r.nextFloat() * high;
+     }
+
     /**
      * Pick a random index from the array, weighted by the value of the
      * corresponding array element.
@@ -120,6 +132,25 @@ public class RandomUtil
      * <tr><td>3</td><td>half of the time</td></tr></table>
      */
     public static int getWeightedIndex (float[] weights)
+    {
+        return getWeightedIndex(weights, rand);
+    }
+
+    /**
+     * Pick a random index from the array, weighted by the value of the
+     * corresponding array element.
+     *
+     * @param weights an array of non-negative floats.
+     * @return an index into the array, or -1 if the sum of the weights
+     * is less than or equal to 0.0 or any individual element is negative. 
+     *
+     * For example, passing in {0.2, 0.0, 0.6, 0.8} will return
+     * <table><tr><td>0</td><td>1/8th of the time</td></tr>
+     * <tr><td>1</td><td>never</td></tr>
+     * <tr><td>2</td><td>3/8th of the time</td></tr>
+     * <tr><td>3</td><td>half of the time</td></tr></table>
+     */
+    public static int getWeightedIndex (float[] weights, Random r)
     {
         float sum = 0.0f;
         for (int ii = 0; ii < weights.length; ii++) {
@@ -132,7 +163,7 @@ public class RandomUtil
         if (sum <= 0.0) {
             return -1;
         }
-        float pick = getFloat(sum);
+        float pick = getFloat(sum, r);
         for (int ii=0, nn=weights.length; ii < nn; ii++) {
             pick -= weights[ii];
             if (pick < 0.0) {