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 values, where the value displayed is incorrect. This has caused me problems 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 installation. 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.

Update – dougg3 has noticed that the issue happens when he uses the IIci ROM, but not if he uses a later (LC 630) ROM.

I have made a small testing tool, which is available for download here :

https://github.com/Phipli/FPUCheckhttps://github.com/Phipli/FPUCheck