Bug report: idiv \ VOGONS

Bug report: idiv

Posted on 2011-11-23, 14:31

bavi Offline

Rank Newbie

Dear developers!

I have found a new error in DOSBox.
The instruction "idiv" crashes DOSBox completely when trying to divide 0x80000000 on 0xFFFF (-0x80000000 on -1):

1mov      dx, 8000h
2mov      ax, 0
3mov      bx, 0FFFFh
4idiv     bx

The expected behaviour is to raise the exception 0.
It seems that the error does not happen with other values.

Would be grateful to fix...

Posted on 2011-11-23, 14:50

wd Offline

Rank DOSBox Author

How does your test application perform on a real system?

Posted on 2011-11-29, 12:32

bavi Offline

Rank Newbie

Well, as I wrote, it raises the exception 0 ("Int 0") when it is run on a real hardware...

I used the following program to find the error:
http://ompldr.org/vYmk4aQ/IDIV_80.zip

It prints "Success" and quits when it is run under pure DOS, but it crashes the emulator when it is run under DOSBox.

Compare with the version which runs normally:
http://ompldr.org/vYmk4Zw/IDIV_80.zip

This is 16-bit division, but maybe the same error exists in the 8-bit and in the 32-bit versions of the instruction.

Posted on 2011-11-29, 14:34

wd Offline

Rank DOSBox Author

Well there it code to care about these cases, don't see anything wrong there at the moment. I'll try to check your code later, thanks for posting it.

Posted on 2011-11-29, 22:08

wd Offline

Rank DOSBox Author

It's only the -MININT/-1 case that's wrong (ie. crashing), is that right?
Causes an arithmetic exception that would have to be checked beforehand.