Re: Best processors for trig?

larwe wrote:
On Mar 30, 1:46 pm, Tim Wescott <t...@xxxxxxxxxxxxxxxx> wrote:

A floating point DSP, as noted.

What's the canonical method of doing this? Taylor series
approximations?

I'm not sure that there is one.

Bringing the argument into range and doing a Taylors series is almost good. Bringing it into range then using a near-Taylors polynomial that takes the truncation into account works better. This works especially well on a VLW instruction set architecture like the 21xx from ADI, because you can perform the x^n in one clock, then the y += ax^n in another -- with sines and cosines you'll out-precise 16-bit data by the time you get to x^6, so you can do the computation in a ridiculously few number of clocks.

If all you want is fast then you can do a humongous table look up.

If you have the room it works _really_ well to do a part lookup, part polynomial expansion algorithm. You have a lot of freedom here to trade off speed for table size.

I have had applications where I did a table look up followed by linear interpolation, and accepted that my trig functions were good to significantly less than 16 bits. If you don't _need_ full precision but you do need speed, this can be very good.

--

Tim Wescott
Wescott Design Services
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