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A tune's tick is the tune's own

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useTune took the period out of a file's header and then Play wrote its
own straight over it, so every tune played at a sixteenth note at 120
beats a minute whatever it asked for. A tune with a #Tick of 0d250000
lasted half as long as it said.

Nothing noticed because every fixture in the suite asked for exactly the
tick Play had written into itself. A test that agrees with the bug by
coincidence is not a test, and the way to find out is a fixture that
wants something else - so slow.tune is two.tune with twice the period and
nothing else changed, and it has to last twice as long.

The period now belongs to whoever supplied the tune: useTune sets it from
the header, useBuiltIn sets its own, and the start code writes only the
control byte - which has to come after either of them, because writing
control with the run bit set is what loads the period.

Found while reading Play to see how a splash screen would drive the
player, which is a reminder that the second reader of a piece of code is
worth more than the first.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
This commit is contained in:
Anachronaut
2026-09-06 09:37:08 -04:00
co-authored by Claude Opus 5
parent 87467a7d3a
commit 6bb1565dea
3 changed files with 47 additions and 9 deletions
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Tests/makedisks.sh
+7
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@@ -736,6 +736,13 @@ open(sys.argv[1], "wb").write(blob(128))
open(sys.argv[2], "wb").write(blob(129))
FIXTURE
"$ROOT/TuneC" -I "$WORK" "$ROOT/Programs/Tunes/two.tune.txt" "$WORK/compiled.tune" >/dev/null
# The same tune at half the speed. A TICK BELONGS TO THE TUNE, and the only reason nothing
# noticed that Play was ignoring it was that every fixture asked for the tick Play happened to
# have written into itself. One that asks for something else is the whole check.
sed 's/#Tick 0d125000/#Tick 0d250000/' "$ROOT/Programs/Tunes/two.tune.txt" > "$WORK/slow.tune.txt"
"$ROOT/TuneC" -I "$WORK" "$WORK/slow.tune.txt" "$WORK/slow.tune" >/dev/null
"$TOOL" put "$DISKS/quiet.img" "$WORK/slow.tune" slow.tune >/dev/null
"$ROOT/Assembler" -I "$ROOT/Programs/Sounds" -I "$ROOT/Programs/Libraries" \
-I "$ROOT/Programs/CosmOS/Source" \
"$ROOT/Programs/CosmOS/Apps/Play.asm" -o "$WORK/Play.sbx" >/dev/null