express.asm

想学习汇编语言的

TITLE Unsigned Arithmetic Expressions        (Express.asm)

INCLUDE Irvine16.inc

.data
msg1 BYTE "Unsigned overflow!",0dh,0ah,0
var1 DWORD 3
var2 DWORD 6
var3 DWORD 4
var4 DWORD ?

.code
main PROC
	mov ax,@data
	mov ds,ax

;Divide Overflow example:

	mov ax,1000h
	mov bl,0
	div bl
	jmp quit


;Example 1: var4 = (var1 + var2) * var3;
Example1:
	mov eax,var1
	add eax,var2
	mul var3			; EAX * var3
	jc  tooBig			; overflow?
	mov var4,eax
	jmp Example2

Example2:  ; var4 = (var1 * 5) / (var2 - 3);

	mov eax,var1
	mov ebx,5
	mul ebx	; EDX:EAX = product
	mov ebx,var2
	sub ebx,3
	div ebx
	mov var4,eax

Example3:   ; var4 = (var1 * -5) / (-var2 % var3);
	mov eax,var2	; begin right side
	neg eax
	cdq	; sign-extend dividend
	idiv var3	; EDX = remainder
	mov ebx,edx	; EBX = right side

	mov eax,-5	; begin left side
	imul var1	; EDX:EAX = left side
	idiv ebx	; final division
	mov var4,eax	; quotient

tooBig:
	mov edx,OFFSET msg1
	call WriteString

quit:
	exit
main ENDP
END main