HP-15C CE woes: 1 bug, 2 limitations, 3 questions

[brouhaha]

(08-09-2023 07:57 PM)brouhaha Wrote:  I believe I've found the 16C microcode instruction which, when BCD addition is improperly optimized by the Nut emulator, causes the decimal integer display problem. I think the corresponding problem in integer to float conversion is in a different microcode path, but I haven't yet checked that.

The binary-to-float error does appear to result from the same instruction. It's in a complicated routine that I don't yet understand, but it appears to be a general-purpose binary-to-BCD conversion. The reason the routine is complicated is probably the need to handle 64-bit input.

Anyhow the (sort of) good news is it looks like only one instruction in the 16C microcode will need special handling in the Nut emulator ARM code to fix both the decimal integer display and tge binary-to-float errors.

I haven't yet checked the 60+80n display error, but it's probably the same instruction.

I have two 15C CE un8ts waiting for me in Colorado, but I'm stuck in Florida for at least a few weeks, so I won't be able to try anything on the 15C CE for a while.