I've tweaked nearly every function in this file, so I'll go through them one by one.
parseDecimal has been reworked a little so that `a` can be used instead of `b` for checking for overflow. I had originally intended to redo it to work like the old parseDecimal, but I think the current method (once reworked a little) is cleaner and smaller, and should be just as fast. 7 bytes and 27 cycles saved.
parseHexadecimal has been changed to load hex digits into `b` `d` `c` `e` from the right (so all the digits move along to the left so the new digit can be inserted on the right), and then only at the end is any shifting done, using the faster `add a, a` to do left shifts. 9 bytes saved and 78 cycles saved inside the loop, and then 49 cycles added after the loop.
parseBinaryLiteral had a few instructions moved around, saving two bytes and 5 cycles inside the loop, and a further 15 cycles saved on error.
parseLiteral has been reworked slightly, the isDigit call has been replaced with an inline parseDecimalDigit, saving a byte and around 20-30 cycles, with around 16 more cycles saved if the number is a decimal. The .char routine has been reduced by a byte, and 6 cycles saved on success, but 5 cycles added on error.
isDigit has been reduced by 4 bytes and 10 cycles on success, with a few more cycles saved on fail (hard to estimate due to branching).
I implement the screen using XCB which is much more friendly
than z80e's SDL+CMake for development machines that want to install
minimal dependencies (for example, a port-less OpenBSD rig).
Sub-parsers are seldom used by themselves, except for parseDecimal.
I'm tightening the code of this unit for two reasons:
1. Optimization
2. Upcoming API change where HL won't be preserved anymore, but will
point to char following the last parse char. This will allow us
to simplify lib/expr.
Instead of going left and right, finding operators chars and replacing them
with nulls, we parse expressions in a more orderly manner, one chunk at a
time. I think it qualifies as "recursive descent", but I'm not sure.
This allows us to preserve the string we parse and should also make the
implementation of parens much easier.
This should make tests a bit more convenient to write and debug.
Moreover, begin de de-IX-ization of parseExpr. I have, in a local WIP, a
parseExpr implemented using a recursive descent algo, it passes all tests, but
it unfortunately assembles a faulty zasm. I have to find the expressions that
it doesn't parse properly.
But before I do that, I prefer to commit these significant improvements I've
been making to tests harness in parallel of this development.
