02-21-2010, 01:48 AM
britlion Wrote:Sometimes we're willing to lose accuracy for speed. ZX BASIC uses the spectrum's ROM routines for many of its math functions, and as a result of them being general purpose routines that use 40 bit numbers, well, they can be a bit slow sometimes.
See my article on square roots, for a good example.
Here is a routine to produce SIN(angle) - where angle is in degrees. It uses a lookup table to calculate sin values, and it's a very quick and dirty method, in that it only actually knows 32 angles, and those to only 8 bit precision. It does linear interpolation between these known angles, however, so that does improve things somewhat.
I was actually surprised how precise it was - it's good for at least 2 decimal places, probably 3 as a rule of thumb. The average error is 0.002 That's probably good enough for games that need to calculate angles. It's about 4-5 times faster than the SIN(FLOAT) function, and not even written in native assembler.
If you need better accuracy, it would be fairly easy to change the method to use a bigger table - perhaps 2 bytes per entry, even.
Remember to work out COS and TAN can also use this function - COS is SIN(90+x) and TAN is SIN(x)/COS(x). It should be easy to write COSINE and TANGENT functions to do the adjustments and call the SINE function.
(And this one I didn't copy. It's all mine! Bugs and all. And now it's free for anyone to use.)
Great :!: :!: :!: :o
I think this should go in the Library/ as Fsin, fcos, ftan, for example??? What do you think?
On the other hand, I think you must be included as a co-author of the ZX Basic framework.
If you are reluctant, please tell me. But your contributions are really importants and you must appear as a coauthor, etc... both in documentation, Wiki, and so on.