Basilisk II Emulator Floating Point Bug

I’m not sure if it is just my specific installation, but I’ve noticed an issue in Basilisk II regarding floating point calculations, where the value calculated is incorrect. This has caused me issues a few times, but this evening, I worked out a partial solution.

The issue seems to be in the FPU emulation itself. I use a IIci ROM in my copy. I found that if I set the CPU to either a full 68040 or a 68030 + FPU floating point values were wildly wrong. I then found that the vanilla “SANE” routines work, so if you set the emulator to 68030 (without an FPU) everything works just fine.

This will slightly reduce software compatibility (although I doubt software that required the FPU would function correctly with the completely incorrect values I was getting), but will mean that software that doesn’t require a hardware FPU will run correctly.