Win32 汇编[24] – 移位: SHL、SHR

SHL、SHR、SAL、SAR: 移位指令


;SHL(Shift Left):             逻辑左移
;SHR(Shift Right):            逻辑右移
;SAL(Shift Arithmetic Left):  算术左移
;SAR(Shift Arithmetic Right): 算术右移

;其中的 SHL 和 SAL 相同, 但 SHR 和 SAR 不同.

;SHL、SAL: 每位左移, 低位补 0,  高位进 CF
;SHR     : 每位右移, 低位进 CF, 高位补 0
;SAR     : 每位右移, 低位进 CF, 高位不变

;它们的结果影响 OF、SF、ZF、PF、CF
;它们的指令格式相同:
SHL r/m, i8
SHL r/m, CL


; Test24_1.asm
.386
.model flat, stdcall

include    windows.inc
include    kernel32.inc
include    masm32.inc
include    debug.inc
includelib kernel32.lib
includelib masm32.lib
includelib debug.lib

.code
main proc
    ;SHL、AL
    mov al, 11100111b
    shl al, 1
    PrintHex al ;CE - 11001110b
    sal al, 2
    PrintHex al ;38 - 00111000b //这里可能有错误
    
    mov al, 11100111b
    mov cl, 2
    shl al, cl
    PrintHex al ;9C - 10011100b
    
    ;SHR
    mov al, 11100111b
    shr al, 2
    PrintHex al ;39 - 00111001b
    
    ;SAR
    mov al, 11100111b
    sar al, 2
    PrintHex al ;F9 - 11111001b
    ret
main endp
end main

ROL、ROR、RCL、RCR: 循环移位指令


;ROL(Rotate Left):                循环左移
;ROR(Rotate Right):               循环右移
;RCL(Rotate through Carry Left):  带进位循环左移
;RCR(Rotate through Carry Right): 带进位循环右移

;ROL: 循环左移, 高位到低位并送 CF
;ROR: 循环右移, 低位到高位并送 CF
;RCL: 循环左移, 进位值(原CF)到低位, 高位进 CF
;RCR: 循环右移, 进位值(原CF)到高位, 低位进 CF

;它们的结果影响 OF、CF
;它们的指令格式相同:
SHL r/m, i8
SHL r/m, CL


; Test24_2.asm
.386
.model flat, stdcall

include    windows.inc
include    kernel32.inc
include    masm32.inc
include    debug.inc
includelib kernel32.lib
includelib masm32.lib
includelib debug.lib

.code
main proc
    ;ROL
    mov al, 11000011b
    rol al, 1
    PrintHex al ;87 - 010000111b
    
    ;ROR
    mov al, 11000011b
    ror al, 1
    PrintHex al ;E1 - 11100001b
    
    ;RCL
    clc
    mov al, 10101111b
    rcl al, 1
    PrintHex al ;5E - 01011110b
    
    stc
    mov al, 10101111b
    rcl al, 1
    PrintHex al ;5F - 01011111b
    
    clc
    mov al, 10101111b
    rcl al, 2
    PrintHex al ;BD - 10111101b //这里可能有错误
    
    ;RCR
    clc
    mov al, 11101011b
    rcr al, 2
    PrintHex al ;BA - 10111010b //这里可能有错误
    ret
main endp
end main

SHLD、SHRD: 双精度移位


;SHLD(Double-Precision Shift Left):  双精度左移
;SHRD(Double-Precision Shift Right): 双精度右移

;SHLD 和 SHRD 有三个操作数
;操作数三: 是移位数目
;操作数一: 是目的操作数
;SHLD 左边被移出的位由操作数二相同数目的高位填充
;SHRD 右边被移出的位由操作数二相同数目的低位填充
;操作数二不变, 且须是寄存器

;它们的结果影响 OF、SF、ZF、PF、CF
;它们的指令格式相同:
SHLD r16/32/m16/m32, r16/32, i8
SHLD r16/32/m16/m32, r16/32, CL


; Test25_3.asm
.386
.model flat, stdcall

include    windows.inc
include    kernel32.inc
include    masm32.inc
include    debug.inc
includelib kernel32.lib
includelib masm32.lib
includelib debug.lib

.code
main proc
    ;SHLD
    mov ax, 1100110011110000b
    mov dx, 1111111100000000b
    shld ax, dx, 2
    PrintHex ax ;33C3 - 0011001111000011b
    
    ;SHRD
    mov ax, 0000111100110011b
    mov dx, 0000000011111111b
    shrd ax, dx, 2
    PrintHex ax ;C3CC - 1100001111001100b
    ret
main endp
end main