x 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 ... 254 255
f(x) 0 0 1 2 3 3 4 5 6 6 7 8 9 9 10 11 12 12 ... 190 191
sta table,y
iny
sta table,y
adc $0
iny
sta table,y
adc $0
iny
sta table,y
adc $0
iny
It's about 2x faster. Your code uses 44 CPU cycles x 64
Edit: plus a branch instruction, maybe that adds 3 cycles x 64 I guess
1) you only need the first 1/4 of the Sine table since the remaining 3/4 are either the first 1/4 in reverse and/or with the sign flipped.
2) and of course Sine can also be used as a Cosine lookup if you add pi/2 radians to the cosine angle (wrapping around of course).
3) to avoid the size needed for a table of floats you can of course use integers (scaled by some factor) or fixed-point values.
4) and simple interpolation would get you seemingly more precision.
(Combining all the above was a bit gross so documentation and a good SPI helped.)
rbanffy•10h ago
They could go one step further and calculate the table as needed and use it as a cache.
For an single image scaling it might get a little bit better.
spc476•8h ago
anyfoo•8h ago
Making it an on-demand cache instead is a neat next step. Whether it helps or hurts depends on the actual input: If the input image uses every pixel value anyway, the additional overhead of checking whether the table entry is computed is just unnecessary extra with no value.
But if a typical image only uses a few pixel values, then the amortized cost of just calculating the few needed table entries may very well be significantly below the cost of the current algorithm.
If images are somewhere in between, or their characteristics not well known, then simply trying out both approaches with typical input data is a good approach!
Unless you’re perfectly happy with 0.2 seconds, for example because the runtime of some other parts take so long that dwarfs those 0.2s, then why bother.
egypturnash•7h ago
If we presume this scaling operation will be done more than one time (which it probably will be if it's getting this level of optimization) then it gets even worse.
anyfoo•2h ago
Of course none of that applies here, but it colors the way you think about things…