; Addition and Subtraction                  (AddSubTest.asm)

; Chapter 4 example. Demonstration of ADD, SUB,
; INC, DEC, and NEG instructions, and how
; they affect the CPU status flags.

.386
.model flat,stdcall
.stack 4096
ExitProcess proto,dwExitCode:dword

.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

    invoke ExitProcess,0
main endp
end main