检索算法---二分查找

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（调整查找范围）
        if (value < items[middle]) {
            stopIndex = middle - 1;
        } else if (value > items[middle]) {
            startIndex = middle + 1;
        }
//recalculate middle（重新计算中项索引）
        middle = Math.floor((stopIndex + startIndex) / 2);
    }
//make sure it's the right value（确保返回正确的值）
    return (items[middle] != value) ? -1 : middle;
}