FORTH for the PC-G850(V)(S)

[robve]

Happy to share that Forth850 v1.0 is now available on GitHub.

The basic 8K version has 295 words. The more complete 11K version has 349 words, including IEEE 754 single precision and a more capable line editor (like Forth500). Both versions were extensively tested and verified *). The performance has not changed since the initial release. The n-queens benchmark is solved in 0.865 seconds.

I wrote three versions of a new IEEE 754 single precision math library with standard floating point operations in Z80 assembly solely using Z80 registers, i.e. "memoryless" **). All trig and other math functions are defined in Forth in MATH.FTH.
- math.asm: a truncating version that is small, 960 bytes of code;
- mathr.asm: a proper rounding version (IEEE 754 round to nearest, ties to even) 1085 bytes;
- mathri.asm: like mathr.asm extended with IEEE INF and NAN (Forth850 does not use INF/NAN) and signed zero, but no subnormals (which are evil), 1286 bytes.

It felt quite satisfying to put this all together, as everything fits in Z80 registers, including shadow, but not IX and IY which remain unused. Some effective use of "Z80 tricks" I learned in the 80s

- Rob

*) while this version was extensively tested and verified, there is no guarantee that there are zero bugs. Please report issues so I can fix them.

**) "memoryless" but a PUSH+POP must be used to copy to Z80 shadow registers, so there is at most one PUSH+POP pair per flop (add, sub, mul, div).