Extending the precision of Woodstock or Saturn based calculators

[Alejandro Paz(Germany)]

Quote:For the HP71, I once considered to increase the width or the A address field from 5 to 6 nibbles, to increase the memory space. But the compatibility problems with the existing firmware were too important, and I gave up.
I also considered a FPU extension.
All I did in my Saturn emulation was (as you know) to add the R5-R7 registers (allowed by the opcode map) and increase the stack depth, although the HP71 firmware was not changed to take benefit of it.

I remember you talked about the extra R registers, I also wondered about the free slots, so to say, in the opcode map.
The increased stack would remove the need for that software stack implementation, it allows for extra 16 levels if I'm not mistaken. I just wonder how many times other software uses it (besides the ROM).

I don't want to add too many unnecessary opcodes but I think there are a couple of tricks being used that could benefit for an extra opcode here and there, like checking if the sign digit is a 9.