This will produce the correct match in most instances but the subtraction can also produce0 so to ensure that a shift is applied in the worst case, if the calculated value is less than1, a minimum shift of one is performed.

• 这在大部分情况中可以产生正确的匹配，但是减法也能产生0，所以为了保证在最坏的情况中也能产生一个移动，如果计算出来的值小于1，至少要产生一个移动。