## sal-shl - shift left

    dest = dest << source

These two instructions are actually the same instruction. sal means shift arithmetic left and shl means shift left, but the result is the same for both. The shl instruction shifts the destination left the number of times indicated by the source. Shifting left by 1 position is equal to multiplying by 2, so the effect equals multiplying by the appropriate power of 2. 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 left:

         1010010010101011
                    <<  3
         ----------------
         0010010101011000

Some examples of using shl:

            shl     rax, 15         ; shift rax 15 bits
            shl     eax, 10         ; shift eax 10 bits
                                    ; fills upper half of rax with 0
            shl     dx, cl          ; shifts dx the cl bits left
                                    ; leaves the rest of rdx alone
            shl     [x], 2          ; shift 32 bit variable x 2 bits

### 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.