TITLE Addition and Subtraction (AddSub3.asm)
; Chapter 4 example. Demonstration of ADD, SUB,
; INC, DEC, and NEG instructions, and how
; they affect the CPU status flags.
; Last update: 2/1/02
INCLUDE Irvine32.inc
.data
Rval SDWORD ?
Xval SDWORD 26
Yval SDWORD 30
Zval SDWORD 40
.code
main PROC
; INC and DEC
mov ax,1000h
inc ax ; 1001h
dec ax ; 1000h
; Expression: Rval = -Xval + (Yval - Zval)
mov eax,Xval
neg eax ; -26
mov ebx,Yval
sub ebx,Zval ; -10
add eax,ebx
mov Rval,eax ; -36
; Zero flag example:
mov cx,1
sub cx,1 ; ZF = 1
mov ax,0FFFFh
inc ax ; ZF = 1
; Sign flag example:
mov cx,0
sub cx,1 ; SF = 1
mov ax,7FFFh
add ax,2 ; SF = 1
; Carry flag example:
mov al,0FFh
add al,1 ; CF = 1, AL = 00
; Overflow flag example:
mov al,+127
add al,1 ; OF = 1
mov al,-128
sub al,1 ; OF = 1
exit
main ENDP
END main
