[Speex-dev] cheb_poly_eva using Clenshaw's recurrence formula

[Jean-Marc Valin]

> > I don't really know if it's a little improvement or not, so I'd like
> > to have feedback from the Speex experts here.

I'd have to test, but it looks right. I don't expect much improvement,
but it makes the code simpler, especially for memory. Would also have to
test on fixed-point and see if it works.

> Maybe a new implementation should use the algorithm above plus the
> explicit ALLOC which is used all over speex (why actually?).

Actually, there would be no need for the ALLOC, which is a good thing.
I'm using ALLOC only for dynamic allocation of temporary variables
(stack) and because not all compilers support C99 arrays.

	Jean-Marc