## sar-shr - shift right

    dest = dest >> source

These two instructions are not the same. With shl 0 bits are always introduced on the left hand side of the value, while sar propagates the sign bit. sar means shift arithmetic right and shr means shift right. The shl instruction shifts the destination right the number of times indicated by the source. Shifting right by 1 position is equal to dividing by 2, so the effect equals dividing by the appropriate power of 2. C/C++ uses sar for signed numbers and shr for unsigned numbers. The destination can be a 64, 32, 16 or 8 bit register or memory location. The source can be either an immediate value or the cl register.

Here is an example of a shift right:

         1010010010101011
                    >>  3
         ----------------
         0001010010010101  ; assuming shl, with shr top 3 bits would be 1

Some examples of using shr and sar:

            shr     rax, 15         ; shift rax 15 bits
                                    ; bits 49:63 will be 0
            sar     eax, 10         ; shift eax 10 bits
                                    ; introduces 10 copies of the sign bit
                                    ; fills upper half of rax with 0
            shr     dx, cl          ; shifts dx the cl bits right
                                    ; introduces cl 0 bits starting at bit 15
                                    ; leaves the rest of rdx alone
            sar     [x], 2          ; shift 32 bit variable x 2 bits
                                    ; introduces 2 copies of the sign bit

### flags: OF CF SF ZF PF

CF contains the last bit shifted out. OF is changed only for single bit shifts. Using CF can be efficient in processing each bit of a register.