Use wrapping behavior on localFile seek position

[weirddan455]

Description

Tested on MS-DOS 6.22 with some ugly looking assembly code I wrote. The return value from seek wraps. If you're at position 10 and you seek backwards by 20, it returns ~4 billion.

Related issues

Fixes #3778

Manual testing

Implementing this behavior fixes the WinG installer. Blackthorne continues to work.

Checklist

Please tick the items as you have addressed them. Don't remove items; leave the ones that are not applicable unchecked.

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[johnnovak]

Nice edge case fix @weirddan455. See, this is where using the integrated debugger would've come in handy 😏

[weirddan455]

Nice edge case fix @weirddan455. See, this is where using the integrated debugger would've come in handy 😏

I don't know that the debugger would have helped. I knew what Dosbox was doing. I needed to confirm what MS-DOS was doing so I had to write a DOS program. I used assembly because NASM can output a .COM file and setting up a DOS C compiler is kind of a pain.

[johnnovak]

I don't know that the debugger would have helped

You could have used your DOS program and inspect the register values in the debugger after a BIOS call, so you could have spared the effort of writing the number to string conversion routine, that's whst I meant.

[weirddan455]

You could have used your DOS program and inspect the register values in the debugger after a BIOS call, so you could have spared the effort of writing the number to string conversion routine, that's whst I meant.

Well I was trying to test in MS-DOS 6.22 in a VM, not inside Dosbox.

[johnnovak]

Well I was trying to test in MS-DOS 6.22 in a VM, not inside Dosbox.

Not sure if you're aware @weirddan455 that you can also run real MS-DOS 6.22 in DOSBox if you mount a FAT HDD partition image. I kinda assumed you did that, that's why I brought up the DOSBox debugger 😄

You can also do freaky stuff like use a dump of a real VGA BIOS instead of our VGA BIOS emulation. I tried it with a few VGA BIOS dumps and it works 😆