ROL              Rotate Left                         Flags: O D I T S Z A P C
*               *
ROL destination,count

                         
  CF        Destination     
                            
                    

ROL shifts the word or byte at the destination to the left by the
number of bit positions specified in the second operand, COUNT. As
bits are transferred out the left (high-order) end of the destination,
they re-enter on the right (low-order) end. The Carry Flag is updated
to match the last bit shifted out of the left end.

If COUNT is not equal to 1, the Overflow flag is undefined. If COUNT
is equal to 1, then the Overflow Flag is set to the XOR of the top 2
bits of the original operand.

                                                                          
Operands                  Clocks   Transfers  Bytes   Example
                        byte(word)
register, 1                 2          -        2     ROL DI,1
register, CL            8 + 4/bit      -        2     ROL BX,CL
memory, 1              15(23) + EA     2       2-4    ROL BYTE,1
memory, CL           20(28)+EA+4/bit   2       2-4    ROL WORD,CL
                                                                          

Notes:         COUNT is normally taken as the value in CL. If,
however, you wish to rotate only one position,
replace the second operand, CL, with the value 1, as
shown in the first example above.

The 80286 and 80386 microprocessors limit the COUNT
value to 31.  If COUNT is greater than 31, these
microprocessors will use COUNT MOD 32 to produce a
new COUNT between 0 and 31.  This upper boundary
exists to limit the amount of time that an interrupt
response will be delayed waiting for the instruction
to complete.

Multiple ROLs that use 1 as the COUNT may be faster
and require less memory than a single ROL that uses
CL for COUNT.

The overflow flag is undefined when the rotate count
is greater than 1.

See also: RCL
See also: ROR
See also: RCR
See also: SAL
See also: SAR
See also: SHL
See also: SHR
See also: EA
See also: Flags

ROL Rotate Left