Speed-coding for the 6502 – a simple example

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.)

    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    

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.