The HP 2000F TSB system doesn't (could not, as it didn't yet exist) support IEEE 754 formats. HP's early design extends from the range of 2−(255−127)−1 to 2+(255−127)−1. The (−1) shown there is because they also don't support hidden bit notation.
I currently don't see a good reason to support denormals or infinities or sNaNs or qNaNs. Slower code would result from handling them and I don't see a good benefit, right now. The old TSB didn't support them, either. So it won't break any existing TSB BASIC code to avoid supporting those extra features.
I do feel okay with supporting hidden bit notation, though. I don't see a problem with that. But I'm unsure on that point, as well.
The question is this:
What may I be I failing to see where it may be important to either (1) drop the idea of supporting hidden bit notation, or (2) add support for denormals or infinities or xNaNs?
In answering, keep in mind that I want to (a) support old HP source code fairly well (but not to the Nth extreme, necessarily), and (b) I'm hoping that extensions (where requested) to support embedded applications will have a solid FP library base to rely upon. So I don't want to build a poor foundation.
P.S. I already know that I'll need to make modifications to the Chebyshev functions they developed – I can't just copy and paste from them. So that may be a price to pay for adding hidden-bit notation. I haven't firmly decided yet whether or not to include hidden bit notation. But I'm looking for reasons, other than having to re-adapt Chebyshev/minimax transcendentals, right now. Any other reasons to consider dropping hidden-bit notation are welcome!
Direct from HP's overview of the 2116 processor:
And SIMH emulating source code.
For those interested in seeing approximately how I'd achieve an FP DIV emulation, I'm providing two cases. Both use a calling convention more aligned with a C compiler than how I will actually write them and they hew closer to IEEE 754 than to HP 2116. They are a single-precision 'loop' MSP430 FP DIV and single-precision 'unrolled loop' MSP430 FP DIV. And they are hereby placed into the public domain.