http://simplemachines.it/doc/arm_inst.pdf
在arm结构中，支持几种位移运算
LSL Logical shift left
LSR Logical shift right
ASR Arithmetic shift right
ROR Rotate right
RRX Rotate right with extend.
LSL LSR ASR
CF <-- Destination <-- 0 0--> Destination --> CF 1st bit --> Destination --> CF
ROR RRX
last bit --> Destination --> CF CF --> Destination --> CF