binarySearch = function(A, value)
    low = 0
    high = A.len - 1
    while true
        if high < low then return null
        mid = floor((low + high) / 2)
        if A[mid] > value then
            high = mid - 1
        else if A[mid] < value then
            low = mid + 1
        else
            return mid
        end if
    end while
end function