Binary search algorithm

Author: Nicholas C. Zakas

algorithms/searching/binary-search/binary-search.js

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+/*
+ * Binary search implementation in JavaScript
+ * Copyright (c) 2009 Nicholas C. Zakas
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+ 
+
+/**
+ * Uses a binary search algorithm to locate a value in the specified array.
+ * @param {Array} items The array containing the item.
+ * @param {variant} value The value to search for.
+ * @return {int} The zero-based index of the value in the array or -1 if not found.
+ */
+function binarySearch(items, value){
+
+    var startIndex  = 0,
+        middle      = Math.floor(items.length / 2),
+        stopIndex   = items.length;
+        
+    while(items[middle] != value && startIndex < stopIndex){
+    
+        //adjust search area
+        if (value < items[middle]){
+            stopIndex = middle - 1;            
+        } else if (value > items[middle]){
+            startIndex = middle + 1;
+        }
+        
+        //recalculate middle
+        middle = Math.floor((stopIndex + startIndex)/2);
+    
+    }
+
+    //make sure it's the right value
+    return (items[middle] != value) ? -1 : middle;
+}