ciolib-win32-gdi divide by zero crash in 43-line/EGA mode (run with '-l43' command-line option)

Unhandled exception at 0x005BCADF in scfg.exe: 0xC000041D: An unhandled exception was encountered during a user callback.

Problem/crash does not happen 100% of the time.

The line of code in scale.c where the exception occurs is

	// If x/y scaling isn't a simple multiple, block scale everything...
	if ((total_yscaling % total_xscaling) == 0) {

	total_xscaling	0	int
	total_yscaling	1	int

Backtrace:

scfg.exe!do_scale(rectlist * rect, int fwidth, int fheight) Line 249
	at c:\sbbs\src\conio\scale.c(249)
scfg.exe!gdi_handle_wm_paint(HWND__ * hwnd) Line 296
	at c:\sbbs\src\conio\win32gdi.c(296)
scfg.exe!gdi_WndProc(HWND__ * hwnd, unsigned int msg, unsigned int wParam, long lParam) Line 579
	at c:\sbbs\src\conio\win32gdi.c(579)
[External Code]
[Frames below may be incorrect and/or missing, no symbols loaded for user32.dll]
scfg.exe!gdi_thread(void * arg) Line 874
	at c:\sbbs\src\conio\win32gdi.c(874)
scfg.exe!invoke_thread_procedure(void(*)(void *) procedure, void * const context) Line 82
	at d:\th\minkernel\crts\ucrt\src\appcrt\startup\thread.cpp(82)
scfg.exe!thread_start<void (__cdecl*)(void *)>(void * const parameter) Line 115
	at d:\th\minkernel\crts\ucrt\src\appcrt\startup\thread.cpp(115)
[External Code]
scfg.exe!__crt_stdio_input::input_processor<wchar_t,__crt_stdio_input::string_input_adapter<wchar_t>>::process_state() Line 1122
	at d:\th\minkernel\crts\ucrt\inc\corecrt_internal_stdio_input.h(1122)

Stepping through the code, I see this calculation:

int yscale = fheight / rect->rect.height;

Results in yscale = 0 (350 / 400).

And then in the if (xscale > yscale) { block, the yscale value (0) is assigned to xscale which is then later assigned to total_xscaling.

Why this problem doesn't happen 100% of the time, I don't know. Perhaps the rect object is shared with another thread?

When it doesn't crash, the fheight parameter value is 400, so yscale is assigned 1 and no divide by zero happens.