Reduce cycles and byte usage #135
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1. Orientation table split & reduced
Previously the orientation table consisted of 12 byte runs, 1 for
each orientation. The 12 bytes consisted of the pattern Y offset,
Tile index, Y offset. This group of 3 was repeated for each of the 4
minos in a piece.
The X/Y offsets have been changed to each have their own table
consisting of 4 byte runs, 1 run for each orientation. The 4 bytes
are for each of the 4 minos in a piece. This means the
multiplication by 12 that was previously needed in
tileModifierForCurrentPiece, isPositionValid and
playState_lockTetrimino has been reduced to a multiplication by 4, a
much simpler operation.
The tiles are also in their own table but the data has been reduced
by 1/4. The currentPiece value is used as-is for lookup into this
table and stored in an aliased temp variable generalCounter5.
2. Use table for Y * 10
Previously the tetriminoY value (and its offsets) would be
multiplied by 10 with shifting/adding. Using multBy10Table was not
an option as the Y value could be either -1 or -2. By pinning
multBy10Table to the beginning of a page and the two negative values
at the end of the page, the table can be used for all potential
values of Y (-2..=20). Assert statements have been added to ensure
that the tables remain where they should be. The orientation tables
and multiplication tables have been placed in between to make use of
nearly the entire page. The page alignment has the additional
benefit of reducing cycle count due to no page boundary crossing.
3. Recycle harddrop's ghost piece sprite staging
The game checks for hard drop prior to the normal shift/rotate/drop.
If the inputs are present for either a hard or sonic drop, the piece
will end up where the ghost piece was staged in the previous frame.
Saving this calculated Y value and reusing it in harddrop_tetrimino
eliminates the redundant repeated calls to isPositionValid.
4. Take advantage of negative bit in Tiles
The minos in use by the game are all positive (7B,7C,7D,7E) while an
empty tile is negative (EF). The negative flag can be used to
quickly determine if there's a mino or not in the playfield.
5. Count down instead of up
A few operations in the hard drop routine handle one row at a time,
either moving it or checking all values. Whether the row is read
left to right or right to left does not matter. By counting down
instead of up, the negative flag can be used to signal the end of
the loop instead of a comparison.
These changes reduce the maximum measured hard drop cycles from 21,876
to 12,877, and the maximum measured ghost piece staging cycles from
9,653 to 7,456. Unused ROM space has been increased from 9,148 bytes
to 9,216.
|
holy shit will have to pull this one and play with it |
Reduces the hard drop maximum cycle count by 39, saves 2 bytes.
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