-----------------------------------------------------------------------------------------------------------------------------------------------------------------

;CBW(Convert Byte to Word):? ? ? 將 AL 擴展為 AX

;CWDE(Convert Word to Extended Double): 將 AX 擴展為 EAX

;CDQ(Convert Doubleword to Quadword): 將 EAX 擴展為 64 位數 EDX:EAX

;CWD(Convert Word to Doubleword):? 將 AX 擴展為 DX:AX

;它們都是用符號位填充多出的空間;它們對 EFLAGS 無影響, 也無參數

-----------------------------------------------------------------------------------------------------------------------------------------------------------------

.code
main proc
??? ;CBW
??? mov al, 7Fh
??? cbw
??? PrintHex ax ;007F
???
??? mov al, 80h
??? cbw
??? PrintHex ax ;FF80
???
??? ;CWDE
??? mov ax, 7FFFh
??? PrintDec ax ;32767
??? cwde
??? PrintHex eax ;00007FFF
??? PrintDec eax ;32767
???
??? mov ax, 8000h
??? PrintDec ax?? ;-32768
??? cwde
??? PrintHex eax ;FFFF8000
??? PrintDec eax ;-32768
???
??? ;CDQ
??? mov eax, 7FFFFFFFh
??? cdq
??? PrintHex edx ;00000000
??? PrintHex eax ;7FFFFFFF
???
??? mov eax, 80000000h
??? cdq
??? PrintHex edx ;FFFFFFFF
??? PrintHex eax ;80000000
???
??? ;CWD
??? mov ax, 7FFFh
??? cwd
??? PrintHex dx ;0000
??? PrintHex ax ;7FFF
???
??? mov ax, 8000h
??? cwd
??? PrintHex dx ;FFFF
??? PrintHex ax ;8000
??? ret
main endp
end main

嗯? 看見沒? 符號數的存儲?? 數據的存儲方式

main proc
??? mov al, 68
??? cbw
??? PrintHex ax ;0044
??? PrintDec ax ;68
???
??? mov al, -68
??? cbw
??? PrintHex ax ;FFBC
??? PrintDec ax ;-68
??? ret
main endp
end main

-----------------------------------------------------------------------------------------------------------------------------------------------------------------

.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
??? ;CBW 等價于 movsx ax, al
??? mov al, 80h
??? cbw
??? PrintHex ax ;FF80
???
??? mov al, 80h
??? movsx ax, al
??? PrintHex ax ;FF80
???
??? ;CWDE 等價于 movsx eax, ax
??? mov ax, 8000h
??? cwde
??? PrintHex eax ;FFFF8000
???
??? mov ax, 8000h
??? movsx eax, ax
??? PrintHex eax ;FFFF8000
??? ret
main endp
end main

?-------------------------------------------------------------------------------------------------------------------

?

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