要求采用快速进位链（Look Ahead）设计一个21位加法器；

2)　　采用结构化的设计方法，所有加法器均采用步骤1）的21位加法器；

3)　　在加法器阵列中加入流水线结构（Pipelinc），输入连续送数，输出连续出结果，流水线填满后每拍输出一个结果；

-1) requires the use of fast carry chain (Look Ahead) design a 21-bit adder

2) the use of structured design methods, all adders are used in step 1) 21-bit adder

3) was added in the adder array pipeline structure (Pipelinc), enter the number of continuous feed, continuous output the results after each shot output lines to fill a result