Most of register fiddling routines (which is now the only thing contained
in care.asm) are used by almost all userspace apps, often in inner loops.
That makes the penalty of using jump tables for those a bit too high.
Moreover, it burdens jump tables needlessly.
Because this unit is very small (now that string routines are out), it makes
sense to always include it in binaries.
* Optimised parsing functions and other minor optimisations
UnsetZ has been reduced by a byte, and between 17 and 28 cycles saved based on branching. Since branching is based on a being 0, it shouldn't have to branch very often and so be 28 cycles saved most the time. Including the initial call, the old version was 60 cycles, so this should be nearly twice as fast.
fmtHex has been reduced by 4 bytes and between 3 and 8 cycles based on branching.
fmtHexPair had a redundant "and" removed, saving two bytes and seven cycles.
parseHex has been reduced by 7 bytes. Due to so much branching, it's hard to say if it's faster, but it should be since it's fewer operations and now conditional returns are used which are a cycle faster than conditional jumps. I think there's more to improve here, but I haven't come up with anything yet.
* Major parsing optimisations
Totally reworked both parseDecimal and parseDecimalDigit
parseDecimalDigit no longer exists, as it could be replaced by an inline alternative in the 4 places it appeared. This saves one byte overall, as the inline version is 4 bytes, 1 byte more than a call, and removing the function saved 5 bytes. It has been reduced from between 52 and 35 cycles (35 on error, so we'd expect 52 cycles to be more common unless someone's really bad at programming) to 14 cycles, so 2-3 times faster.
parseDecimal has been reduced by a byte, and now the main loop is just about twice as fast, but with increased overhead. To put this into perspective, if we ignore error cases:
For decimals of length 1 it'll be 1.20x faster, for decimals of length 2, 1.41x faster, for length 3, 1.51x faster, for length 4, 1.57x faster, and for length 5 and above, at least 1.48x faster (even faster if there's leading zeroes or not the worst case scenario).
I believe there is still room for improvement, since the first iteration can be nearly replaced with "ld l, c" since 0*10=0, but when I tried this I could either add a zero check into the main loop, adding around 40 cycles and 10 bytes, or add 20 bytes to the overhead, and I don't think either of those options are worth it.
* Inlined parseDecimalDigit
See previous commit, and /lib/parse.asm, for details
* Fixed tabs and spacing
* Fixed tabs and spacing
* Better explanation and layout
* Corrected error in comments, and a new parseHex
5 bytes saved in parseHex, again hard to say what that does to speed, the shortest possible speed is probably a little slower but I think non-error cases should be around 9 cycles faster for decimal and 18 cycles faster for hex as there's now only two conditional returns and no compliment carries.
* Fixed the new parseHex
I accidentally did `add 0xe9` without specifying `a`
* Commented the use of daa
I made the comments surrounding my use of daa much clearer, so it isn't quite so mystical what's being done here.
* Removed skip leading zeroes, added skip first multiply
Now instead of skipping leading zeroes, the first digit is loaded directly into hl without first multiplying by 10. This means the first loop is skipped in the overhead, making the method 2-3 times faster overall, and is now faster for the more common fewer digit cases too. The number of bytes is exactly the same, and the inner loop is slightly faster too thanks to no longer needing to load a into c.
To be more precise about the speed increase over the current code, for decimals of length 1 it'll be 3.18x faster, for decimals of length 2, 2.50x faster, for length 3, 2.31x faster, for length 4, 2.22x faster, and for length 5 and above, at least 2.03x faster. In terms of cycles, this is around 100+(132*length) cycles saved per decimal.
* Fixed erroring out for all number >0x1999
I fixed the errors for numbers >0x1999, sadly it is now 6 bytes bigger, so 5 bytes larger than the original, but the speed increases should still hold.
* Fixed more errors, clearer choice of constants
* Clearer choice of constants
* Moved and indented comment about fmtHex's method
* Marked inlined parseDecimalDigit uses
* Renamed .error, removed trailing whitespace, more verbose comments.
* addHL and subHL affect flags, and are smaller
Most importantly, addHL and subHL now affect the flags as you would expect from a 16 bit addition/subtraction. This seems like it'd be preferred behaviour, however I realise any code relying on it not affecting flags would break. One byte saved in addHL, and two bytes saved in subHL. Due to the branching nature of the original code, it's difficult to compare speeds, subHL is either 1 or 6 cycles faster depending on branching, and addHL is between -1 and 3 cycles faster. If the chance of a carry is 50%, addHL is expected to be a cycle faster, but for a chance of carry below 25% (so a < 0x40) this will be up to a cycle slower.
* Update core.asm
* Reworked one use of addHL
By essentially inlining both addHL and cpHLDE, 100 cycles are saved, but due to the registers not needing preserving, a byte is saved too.
* Corrected spelling error in comment
* Reworked second use of addHL
43 cycles saved, and no more addHL in critical loops. No bytes saved or used.
* Fixed tabs and spacing, and made a comment clearer.
* Clearer comments
* Adopted push/pop notation
Pretty major improvements to both of these, cpHLDE is now 5 bytes shorter and between 9 and 12 cycles faster due to branching, and writeHLinDE is now 2 bytes shorter and 21 cycles faster.
* Optimised intoXX functions
Rewrote intoXX functions to mainly rely on intoHL, as the HL instructions are smaller and faster. Also removed some redundant push and pop instructions. I edited the given unit tests to test these, and they seem to work as expected.
* Doesn't use self-modifying code
The number of bytes is the same as my previous attempt, with 11 more cycles in intoHL, so although I don't feel as clever this time it's still a good optimisation. I found an equivalent method for intoDE, however relying on intoHL still allows for `ex (sp), hl` to be used in intoIX, which is smaller and faster.
* Update core.asm
* Tried harder to follow coding convention
Added tabs between mnemonics and operands, and replaced a new line I accidentally removed.
This huge refactoring remove the Seek and Tell routine from blockdev
implementation requirements and change GetC and PutC's API so that they
take an address to read and write (through HL/DE) at each call.
The "PTR" approach in blockdev implementation was very redundant from
device to device and it made more sense to generalize. It's possible
that future device aren't "random access", but we'll be able to add more
device types later.
Another important change in this commit is that the "blockdev handle" is
now opaque. Previously, consumers of the API would happily call routines
directly from one of the 4 offsets. We can't do that any more. This
makes the API more solid for future improvements.
This change forced me to change a lot of things in fs, but overall,
things are now simpler. No more `FS_PTR`: the "device handle" now holds
the active pointer.
Lots, lots of changes, but it also feels a lot cleaner and solid.
This allows us to break through the 64K limit for includes CFS in zasm,
a limit we were dangerously close to breaking. In fact, this commit
makes us go over that limit. Right in time!
Very incomplete, but if you play your cards right, you can, with the
shell:
1. Create a new CFS
2. Mount it
3. Allocate a file with an arbitrary name
4. Have it listed with `fls`
Instead of waiting, GetC always return immediately, with Z indicating if
something was fetched. The "wait" loop is implemented by the called (and
in the new `blkGetCW`).
This simplifies out-of-bounds verifications for storage blockdevs.
They serve a different purpose. The goal of the ACIA buffer is to ensure
that we don't miss an input. The goal of the shell buffer is to wait
until the user presses return.
The ACIA buffer has been moved to shell and replaced with a circular
buffer, a more appropriate data structure for this kind of purpose.
Also, introduce `aciaGetC`.
Virgil Dupras