seek

代码说明：

说明：  乘积的最后三位的值只与乘数和被乘数的后三位有关，与乘数和被乘数的高位无关，利用此来求尾数(The last three values of the product only with the multiplier and the multiplicand on the back three, with a high multiplier and the multiplicand has nothing to do, take advantage of this to seek mantissa)