汇编-CWD将有符号数字转换为双字

将ax寄存器中的有符号数扩展为dx:ax中的有符号数。如果ax是正数，则dx会被设置为00000000h；如果ax是负数，则dx会被设置为FFFFFFFFH 

.386  
.model flat,stdcall 
option casemap:none
.stack 4096

Include Irvine32.inc
includelib Irvine32.lib

ExitProcess PROTO,dwExitCode:DWORD  
 
.data   
packed_1 WORD 4536h 
packed_2 WORD 7207h 
sum DWORD ?

 
.code   
main PROC   
    
    
    mov ax,-5  ;dx=xxh   ax=FFFBh
    CWD
    ;DX = FFFFh     AX = FFFBh



    INVOKE ExitProcess,0  
main ENDP   
END main