加法器與合成

CSA is an adder architecture used to calculate intermediate partial sum values.
CSA architecture saves the entire carry vector to avoid carry-propagation delay overhead.
A tree structure of CSAs is typically used to reduce the number of input vectors from N down to 2.
A conventional adder (ripple, cla, clf) is required at the bottom of the CSA tree to add the final 2
vectors and produce the final sum.


















如果有特殊的加法器需求，就只好用DesignWare
列表如下
- Serial-prefix (rpl)
- Flexible carry-select
- Kogge-Stone parallel-prefix
- Mux-based prefix circuit
- Use of inverting full-adder cells
- Sklansky parallel-prefix