资料来源 : Free On-Line Dictionary of Computing

modular arithmetic
     
         (Or "clock arithmetic") A kind of integer
        arithmetic that reduces all numbers to one of a fixed set
        [0..N-1] (this would be "modulo N arithmetic") by effectively
        repeatedly adding or subtracting N (the "modulus") until the
        result is within this range.
     
        The original mathematical usage considers only _equivalence_
        modulo N.  The numbers being compared can take any values,
        what matters is whether they differ by a multiple of N.
        Computing usage however, considers modulo to be an operator
        that returns the remainder after integer division of its first
        argument by its second.
     
        Ordinary "clock arithmetic" is like modular arithmetic except
        that the range is [1..12] whereas modulo 12 would be [0..11].
     
        (2003-03-28)