Re: Best processors for trig?

On 31 Mar 2007 07:55:02 -0700, "Mike Noone" <nleahcim@xxxxxxxxx>
wrote:

On Mar 30, 11:46 am, Tim Wescott <t...@xxxxxxxxxxxxxxxx> wrote:
Mike Noone wrote:
Hi - I was just wondering, are there any processors out there that
have been optimized for trig operations? I'm hoping to find a
processor that can do trig ops (sin, cos, tan, asin, acos, atan, etc.)
quickly. The faster the better. I would really like to be able to do
such operations in the single digit microsecond range or less, though
that's probably a longshot. I'm looking for floating point values -
ideally in the C data type "double". Does anything like this exist?
Ideally in a non-BGA package, as I hate debugging the little buggers.

Thanks!

-Mike

A floating point DSP, as noted.

Pentium-class x86 processors, although that's stretching the idea of
"embedded" a bit.

Probably PowerPC architecture chips, at least the ones with FPUs (look
carefully, however, I bet there are ones with simple FPUs and others
with complex FPUs).

Some of the bigger fixed-point DSPs may be able to do this -- I know
that TI's '28xx family will do floating point quite efficiently, but (a)
I know they do it by leaving out some of the corner-case testing for
exceptions and (b) I don't know how this translates to trig performance.

Tim Wescott

Why the 28x family? Wouldn't it make more sense to use a 67x as it is
designed for floating point, while the 28x is designed for fixed
point?

I must admit that I am new to the DSP world, so it's quite possible
I'm missing something obvious here.

Unless you are especially interested in values _very_ close to 0 and
90 degrees (or perhaps 45 degrees for expressions like (tan(45)-1),
why would you use floating point arithmetics ?

If you are really interested in such special cases, it usually
indicates that doing some additional math would solve the problem
without using trigonometric functions at all.

Anyway, by dividing the argument range into sufficiently small
segments, the problem can be solved by 6th..8th degree polynomial,
thus any DSP with Multiply-Add instructions are very handy.

Paul

.

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