8086 Assembly Program for Subtraction of Two 32 bit Numbers

data segment
abc dd 9ABCDEF0h
def dd 12345678h
ghi dw ?
data ends

code segment
assume cs:code, ds:data
mov ax,data
mov ds,ax
mov dl,00h
mov ax, word ptr abc
mov bx, word ptr def
sub ax,bx
mov word ptr ghi,ax
mov ax, word ptr abc+2
mov bx, word ptr def+2
sbb ax,bx
mov word ptr ghi+2,ax
jnc move
inc dl
move: mov byte ptr ghi+4,dl
int 3
code ends
end start


C:\TASM>masm an32sub.asm
Microsoft (R) Macro Assembler Version 5.00
Copyright (C) Microsoft Corp 1981-1985, 1987.  All rights reserved.

Object filename [an32sub.OBJ]:
Source listing  [NUL.LST]:
Cross-reference [NUL.CRF]:

  50288 + 450368 Bytes symbol space free

      0 Warning Errors
      0 Severe  Errors

C:\TASM>link an32sub.obj

Microsoft (R) Overlay Linker  Version 3.60
Copyright (C) Microsoft Corp 1983-1987.  All rights reserved.

Run File [AN32SUB.EXE]:
List File [NUL.MAP]:
Libraries [.LIB]:
LINK : warning L4021: no stack segment

C:\TASM>debug an32sub.exe

AX=8888  BX=1234  CX=0038  DX=0000  SP=0000  BP=0000  SI=0000  DI=0000
DS=0B97  ES=0B87  SS=0B97  CS=0B98  IP=0027   NV UP EI NG NZ NA PE NC
0B98:0027 CC            INT     3
-d 0B97:0000
0B97:0000  F0 DE BC 9A 78 56 34 12-78 88 88 88 00 00 00 00   ....xV4.x.......
0B97:0010  B8 97 0B 8E D8 B2 00 A1-00 00 8B 1E 04 00 2B C3   ..............+.
0B97:0020  A3 08 00 A1 02 00 8B 1E-06 00 1B C3 A3 0A 00 73   ...............s
0B97:0030  02 FE C2 88 16 0C 00 CC-63 83 C4 06 FF 36 24 21   ........c....6$!
0B97:0040  B8 0A 00 50 E8 47 5E 83-C4 04 5E 8B E5 5D C3 90   ...P.G^...^..]..
0B97:0050  55 8B EC 81 EC 84 00 C4-5E 04 26 80 7F 0A 00 74   U.......^.&....t
0B97:0060  3E 8B 46 08 8B 56 0A 89-46 FC 89 56 FE C4 5E FC   >.F..V..F..V..^.
0B97:0070  26 8A 47 0C 2A E4 40 50-8B C3 05 0C 00 52 50 E8   &.G.*[email protected].

2 thoughts on “8086 Assembly Program for Subtraction of Two 32 bit Numbers”

  1. Doesn’t work in the case of smaller number – larger number:

    ; 32 bit subtraction
    ; _______________

    assume cs:code, ds:data

    data segment
    opr1 dd 0ffffffffh
    opr2 dd 00000001h
    res dd 00000000h
    car db 00h
    data ends

    code segment
    org 0100h

    start: mov ax, data
    mov ds, ax
    mov ch, 00h
    mov ax, word ptr opr1
    mov bx, word ptr opr2
    sub ax, bx
    jnc here1
    neg ax

    here1: mov word ptr res, ax
    mov ax, word ptr opr1 + 2
    mov bx, word ptr opr2 + 2
    sbb ax, bx
    jnc here2
    neg ax
    inc ch

    here2: mov word ptr res+2, ax
    mov byte ptr res+4, ch
    mov ah, 4ch
    int 21h

    code ends

    end start

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