Order lists hold one-byte sequence indices and 0x80 holds a one-byte
patch index. Two tables, PatchTable and SequenceTable, are the only
places an address lives.
THAT IS WHAT MAKES A TUNE LOADABLE WITHOUT WALKING IT. Nothing inside a
sequence or an order list is an address, so putting one in memory means
adding the load address to two arrays and nothing else. The alternative
is a loader that parses every sequence looking for addresses to correct,
which is a loader a malformed file can walk off a cliff.
Doing it now, while the tune is still assembled in, means the file form
and the assembled form are the same shape - so reading a tune from a file
will change no engine code at all. The whole point of the rung.
The patch each voice starts on moved from four calls in a row into
VoiceStart, four declared bytes, and loadStartPatches reads them. A
starting instrument is state and belongs where state goes: the user's
ruling is that a voice with undefined state is an error, prompted by
noticing that a program run a second time starts with the memory the
first run left, because loading is what initialises and running is not.
Order lists also halved in size, which was not the reason but is welcome.
Hand-writing the two tables is exactly the tedium the compiler exists to
remove - every sequence counted into its place, and moving one means
renumbering. Better to feel that here than after a tool has baked the
shape in.
Verified by rendering: bar for bar the same piece. break.sh confirms the
scaling, since an index is doubled to reach a two-byte entry and halving
that step lands on the wrong sequence and fails four checks.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
The rung between M3 and M4, and the point of doing it before the format:
the engine learns the tracker's model with the tune still assembled in,
so M4 becomes serialising a thing that exists rather than designing a
thing that does not.
A voice no longer walks one long track. 0xFF now means THIS SEQUENCE
ended, and the voice takes the next address from an order list of its
own. That is where repetition comes from, and it costs no notation: the
bass plays the same sequence in the first bar and the last and it is
written once. Per voice rather than one shared table of four-column rows,
because a voice's order cursor is then a pointer it advances by itself -
the same LDD and STD move everything else here makes. Four columns is how
it reads, not how it is stored.
Sequences also carry COMMANDS, which take no tick: the reader acts and
reads the next event on the same boundary. One is defined, 0x80, which
plays the rest of that voice on another patch, and the other 125 values
are left alone. A patch change reshapes whatever is still ringing on the
voice and nothing can be done about that - a channel has one set of
parameters and a note in its release is using them - so it is a fact
about the hardware and the cure is a rest, which is the composer's.
The engine moved to Libraries/player.asm rather than being copied into
the test a second time, now that it is big enough to drift. Play supplies
the tune and the beat; the library supplies the scheduler, the patch
loader and a voice's state. Verified by rendering: bar for bar identical
across the move.
AND THE TEST FOUND A REAL FLAW IN THE FORMAT, which is the whole argument
for building the reader first. The order list ended with 0x0000, on the
reasoning that no sequence could live below the 0x3000 this program is
based at. True of a loaded program, false of a boot image whose data
starts at zero - so the first test written against it read its own first
sequence as the end of the list and played nothing at all. It is 0xFFFF
now, which mirrors the 0xFF ending a sequence and is impossible
everywhere: a sequence at 0xFF00 or above has fewer bytes left than it
needs. An address is a poor place to hide a flag unless the address is
impossible in every program, not just this one.
One order list in the test now really ends, because otherwise nothing
reached the terminator at all: every voice sat on a long rest and the
break went unnoticed. With it, breaking the test reads garbage past the
end and the counter sums two notes at 781 hertz.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
a * b = qs[a + b] - qs[|a - b|] where qs[n] is n squared over four
because (a+b)^2/4 minus (a-b)^2/4 is exactly a*b, and the halves the
flooring throws away cancel between the two terms. A multiply is two
lookups and a subtract.
AND THE TABLE IS BUILT BY ADDING, which is the part that makes it fit a
machine with no multiplier at all. A table of squares would need squaring
to fill; this one does not, because qs[n] = qs[n-1] + n/2, and n/2 goes 0,
1, 1, 2, 2, 3 - a number that steps up on every even n. So the whole thing
is a running total and a toggle, and nothing harder than an add appears
anywhere in building the thing that does the multiplying.
511 entries of two bytes, because a byte plus a byte reaches 510. That is
1,022 bytes of Data Memory, and it is the price: a kilobyte traded for an
operation the hardware has not got.
The operands go in memory rather than in registers. B cannot be stored and
a product does not fit in one byte anyway, so two in and two out would
spend more instructions shuffling than the multiply costs.
Checked against nought, the commutation both ways round, a square, and 255
times 255 - which is 0xFE01 and the largest product two bytes hold. The
square is the case the identity leans on hardest: the difference term is
nought and the whole answer comes out of one entry.
Wanted for Lunar Porter's orbit, where the trade between height and speed
has to be proportional to vx times vy and could not be. Useful well beyond
it: this is the routine every fixed point sum on this machine has been
doing without.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
Twenty four places moved Q into A or B by pushing it and popping it back.
That is four bus cycles and two bytes to do what MVQA does in one of each,
and several of them are inside loops - Life, the calculator, int8. Nineteen
more loaded zero with INIA 0d0 where RSTA says the same thing in one byte.
Both are equivalent at the CPU rather than by assertion: RSTA and INIA both
leave Status alone, and PSHQ followed by POPA nets to A = Q with the Stack
Pointer where it started. The one difference is that the pair leaves a copy
of Q in memory just below the Stack Pointer and MVQA does not, which
nothing here reads.
Five recorded outputs moved and every one of them says the change worked:
- 16x16Life fits five more generations into the same cycle budget, the
first 457 lines identical, because the loop got cheaper.
- Life.sbx is 1409 bytes rather than 1411, in three tests that list it.
- Edit.sbx is 1995 rather than 1996.
That last one broke a check I added this morning, and the hole is worth
recording: the CosmOS README's claim about Edit's size did not have the
word "Edit" on the same line as the number, because the subject was in the
sentence before, so the check that measures quoted sizes skipped it
silently. The sentence now names what it is talking about, which makes it
both checkable and clearer, and the check fails on a wrong number there.
Comments on either half of a replaced pair are carried onto the
instruction that replaces them, so nothing anybody wrote was lost.
Thirteen build artifacts were tracked: ten .bin files, a disk image, and the
text file that had been put on it. Every one is produced by 'make' in
Programs/ from a source file that is also tracked.
NINE OF THE TEN BINARIES DISAGREED WITH THEIR OWN SOURCE, including
Programs/CosmOS/Bin/cosmos.bin - the operating system. Only hello.bin still
matched, and that by accident.
That is worse than shipping no binary at all. A repository holding both a
source file and a stale build of it has two answers to what a program does,
and the wrong one is the one that runs. Somebody reads the source, runs the
binary, and sees behaviour that is not in the code with nothing to tell them
why.
Nothing referenced any of them - not the makefiles, not the tests, not the
manuals. Checked before removing, and checked after: the suite passes, and a
clean clone with all of them gone builds both tools and assembles every
program from source alone.
.gitignore now covers *.bin, *.sbx and *.img, unanchored, because a build
output may appear anywhere a source file lives.
Programs/CosmOS/Bin/ held cosmos.bin, disk.img and a 17 byte hello.txt that
existed only to be put on that image. It was a snapshot of a demo from
before Tests/makedisks.sh built its own fixtures, and it goes with them.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
Added DPUP and DPDN, which take a one byte operand specifying how far up or down to offset the Data Pointer.
Three Fibonacci generators using the print.asm library.
- 8 bit values printing in decimal representation.
- 16 bit values printing in hexadecimal representation.
- 32 bit values printing in hexadecimal representation.
AnachronautandClaude Opus 5
Anachronaut