function binary_search_iterative(a, value) {
    lo = 0;
    hi = a.length - 1;
    while (lo <= hi) {
        var mid = Math.floor((lo+hi)/2);
        if (a[mid] > value)
            hi = mid - 1;
        else if (a[mid] < value)
            lo = mid + 1;
        else
            return mid;
    }
    return null;
}