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(nasm.info)Section B.4.275

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B.4.275. `ROL', `ROR': Bitwise Rotate
-------------------------------------

     ROL r/m8,1                    ; D0 /0                [8086]
     ROL r/m8,CL                   ; D2 /0                [8086]
     ROL r/m8,imm8                 ; C0 /0 ib             [186]
     ROL r/m16,1                   ; o16 D1 /0            [8086]
     ROL r/m16,CL                  ; o16 D3 /0            [8086]
     ROL r/m16,imm8                ; o16 C1 /0 ib         [186]
     ROL r/m32,1                   ; o32 D1 /0            [386]
     ROL r/m32,CL                  ; o32 D3 /0            [386]
     ROL r/m32,imm8                ; o32 C1 /0 ib         [386]

     ROR r/m8,1                    ; D0 /1                [8086]
     ROR r/m8,CL                   ; D2 /1                [8086]
     ROR r/m8,imm8                 ; C0 /1 ib             [186]
     ROR r/m16,1                   ; o16 D1 /1            [8086]
     ROR r/m16,CL                  ; o16 D3 /1            [8086]
     ROR r/m16,imm8                ; o16 C1 /1 ib         [186]
     ROR r/m32,1                   ; o32 D1 /1            [386]
     ROR r/m32,CL                  ; o32 D3 /1            [386]
     ROR r/m32,imm8                ; o32 C1 /1 ib         [386]

   `ROL' and `ROR' perform a bitwise rotation operation on the given
source/destination (first) operand. Thus, for example, in the operation
`ROL AL,1', an 8-bit rotation is performed in which `AL' is shifted
left by 1 and the original top bit of `AL' moves round into the low bit.

   The number of bits to rotate by is given by the second operand. Only
the bottom five bits of the rotation count are considered by processors
above the 8086.

   You can force the longer (286 and upwards, beginning with a `C1'
byte) form of `ROL foo,1' by using a `BYTE' prefix: `ROL foo,BYTE 1'.
Similarly with `ROR'.