MPS Lectures - Chapter 3

Figure 3-51 Shift and rotate instructions.

Name	Mnemonic and Format	Description*

Shift logical left	SHL OPR,CNT
Shift arithmetic left	SAL OPR,CNT	Same as SHL
Shift logical right	SHR OPR,CNT
Shift arithmetic right	SAR OPR,CNT
Rotate left	ROL OPR,CNT	LSB of result = CF
Rotate right	ROR OPR,CNT	MSB of result = CF
Rotate left through carry	RCL OPR,CNT
Rotate right through carry	RCR OPR,CNT

*Number of bit positions shifted is determined by CNT

Flags: CF flag set as indicated. PF, SF, and ZF flags are set by shift instructions but left unchanged by the rotate instructions. OF flag is meaningful only if count is 1. AF flag is affected by shift instruction, but has no meaning.

Addressing modes: OPR can have any mode except immediate; CNT must be 1 or CL.

Figure 3-52 Examples of shift and rotate instructions.

Initially:
     (DL) = 10001101
     (CL) = 00000011
     (CF) = 1


Instruction                        Results

SHL    DL,CL        CF = 0        01101000
SAL    DL,CL        CF = 0        01101000
SHR    DL,CL                      00010001        CF = 1
SAR    DL,CL                      11110001        CF = 1
ROL    DL,CL        CF = 0        01101100
ROR    DL,CL                      10110001        CF = 1
RCL    DL,CL        CF = 0        01101110
RCR    DL,CL                      01110001        CF =1

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