Division of double word in MASM

Question

 HDIVIDEND DW 1234H
 LDIVIDEND DW 5678H
 DIVISOR DW 1234H

MOV AX,LDIVIDEND
MOV DX,HDIVIDEND
DIV DIVISOR

I am getting an "Illeagal instruction" on running a masm code at the instruction

 DIV DIVISOR

Where HDIVIDEND is the higher order bytes of dividend in 16 bit. And divisor is 16 bit.

Answer 1

Yes, the program you had written should have assembled correctly. Perhaps you had made a mistake in another part of your file, which would thus be the cause of your "illegal instruction". Or maybe you should download a newer version of MASM as it might have temporarily malfunctioned. Anyway, here is the working code, assembled and linked with MASM64 for Windows (should still work with MASM32):

dseg            segment         para 'DATA'
hdividend       dw              1234h
ldividend       dw              5678h
divisor         dw              1234h
dseg            ends

cseg            segment         para 'CODE'
start           proc
                mov             ax,             ldividend
                mov             dx,             hdividend
                div             divisor
start           endp
cseg            ends
                end

And the output:

C:\Masm64>bin\ml64.exe /c division.asm

Microsoft (R) Macro Assembler (x64) Version 8.00.50727.215
Copyright (C) Microsoft Corporation.  All rights reserved.

Assembling: division.asm

C:\Masm64>bin\link.exe /subsystem:windows /entry:start division.obj
Microsoft (R) Incremental Linker Version 8.00.50727.215
Copyright (C) Microsoft Corporation.  All rights reserved.

Hope this helps.