一种可配置的桶式移位器的设计

DESIGN OF A CONFIGURABLE BARREL SHIFTER

根据 CPU中指令的不同 ,实现了一种可配置的桶式移位器 ,可以将移位器配置为通用移位器或对位移位移位器 .采用这种桶式移位器 ,可以使采用部分译码方式的移位器在原有功能的基础上增加对位右移的功能 ,并同时产生满足 IEEE舍入要求的附加位 .在增加少量控制逻辑的基础上 ,使浮点运算的对位移位器与定点运算实现移位操作的通用移位器合二为一 ,增强了桶式移位器的可复用性 ,减少了 CPU芯片的面积 ,不需增加关键路径的长度 ,电路布线规整 ,易于 VL

Most of general processor chips have a barrel shifter, which performs all kinds of shifter operations in one clock cycle. A new circuit design method is proposed in the paper, which implements a configurable barrel shifter. It can be used as general shifter or alignment shifter. By using the method, the partial decoded barrel shifter is of functions of alignment shifter with additional bits for rounding and general shifter. Based on a few of control logic, the barrel shifter can be reused, and at the same time circuit scale and critical path delay is decreased. In addition, it is easy to use the regular routing is feasible to implement VLSI.