Suppose that one byte in a buffer covered by the Internet checksum algorithm needs to be decremented (e. g., a header hop count field).
Give an algorithm to compute the revised checksum without rescanning the entire buffer. Your algorithm should consider whether the byte in question is low order or high order.
You can assume that you are given n the original checksum, the position of the byte which is to be decremented and the value by which the byte will be decremented.