Shift and Rotate Instructions
Shift and rotate instructions in assembly language are used to manipulate the bits of data in registers. These instructions allow you to shift or rotate the bits left or right, facilitating various bitwise operations. Here are some common shift and rotate instructions:
Shift Instructions:
Shift Left Logical (SHL or SAL):
Shifts the bits of a register or memory operand to the left by a specified number of positions. Zeros are shifted into the vacated bit positions. The carry flag is affected.
assembly
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SHL AX, 1 ; AX = AX 1
Shift Right Logical (SHR):
Shifts the bits of a register or memory operand to the right by a specified number of positions. Zeros are shifted into the vacated bit positions. The carry flag is affected.
assembly
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SHR BX, 2 ; BX = BX 2
Rotate Instructions:
Rotate Left (ROL):
Rotates the bits of a register or memory operand to the left by a specified number of positions. The bits shifted out on the left are rotated into the right. The carry flag is affected.
assembly
Copy code
ROL CL, 3 ; Rotate the bits in CL to the left by 3 positions
Rotate Right (ROR):
Rotates the bits of a register or memory operand to the right by a specified number of positions. The bits shifted out on the right are rotated into the left. The carry flag is affected.
assembly
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ROR DX, 4 ; Rotate the bits in DX to the right by 4 positions
Example:
assembly
Copy code
section .data
section .text
global _start
_start:
; Shift Left Logical (SHL)
MOV AX, 0b11001100 ; Binary: 11001100
SHL AX, 1 ; Shift left by 1 position
; Result: 0b10011000 (AX = 0x98)
; Shift Right Logical (SHR)
MOV BX, 0b10101010 ; Binary: 10101010
SHR BX, 2 ; Shift right by 2 positions
; Result: 0b00101010 (BX = 0x2A)
; Rotate Left (ROL)
MOV CL, 0b11110000 ; Binary: 11110000
ROL CL, 3 ; Rotate left by 3 positions
; Result: 0b10000111 (CL = 0x87)
; Rotate Right (ROR)
MOV DX, 0b00110011 ; Binary: 00110011
ROR DX, 2 ; Rotate right by 2 positions
; Result: 0b11001100 (DX = 0xCC)
; Further code goes here...
; Exit the program
MOV EAX, 1 ; System call number for exit
XOR EBX, EBX ; Exit code 0
INT 0x80 ; Invoke the kernel
In this example, the shift and rotate instructions manipulate binary data in registers (AX, BX, CL, and DX). The results demonstrate the effects of shifting and rotating bits based on the specified positions.
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