binary search

binary search.js

/**
 * 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,
        stopIndex   = items.length - 1,
        middle      = Math.floor((stopIndex + startIndex)/2);
        
    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;
}