A couple of things:

1. I'm pretty sure any error in cos at pi and 2pi will be smaller in double precision than float's epsilon, so I don't think that there's any need to set -1.0 and 1.0 explicitly after all except to be extra safe. However, at pi/2 and 3pi/2 the error is still larger than the minimum normal number, so it is worth setting the zero crossings to 0.0.

2. For garray_dofo() there isn't a great way of using explicit 0.0 at zero crossings without incurring an extra check, like don't add to the sum if absolute value is less than e.g. 1.0e-10. For this, probably just using M_PI and incrementing integer phase like for the cosine table is enough.

On Wed, Jun 5, 2024 at 2:20 PM Alexandre Torres Porres <porres@gmail.com> wrote:

Em qua., 5 de jun. de 2024 às 14:31, Matt Barber <brbrofsvl@gmail.com> escreveu:
While we're at it, I think it would be worth tuning garray_dofo() to use the same so that sinesum and cosinesum have the same level of accuracy, guarantees of symmetry, etc.

MB

Good catch! In fact, I think this is a great opportunity to also fix this bug https://github.com/pure-data/pure-data/issues/371 which is totally related. I just reopened https://github.com/pure-data/pure-data/issues/105 as well as I'm still considering the table could/should be still "perfectly symmetric" considering 0 crossings and the start/end points.
On Wed, Jun 5, 2024 at 12:52 PM Alexandre Torres Porres <porres@gmail.com> wrote:
For the record and sake of comparison, Cyclone uses a 16384 points table, and linear interpolation, calculated with double precision. We did this because MAX documents it uses such a table, and we made it (well, Matt did) simetric.

I see Pd is doing kind of the same, huh? linear interpolation on a table calculated with double precision.

I see SuperCollider mentions it uses 8192 points and linear interpolation on its oscillator.

I guess MAX is exaggerating its table size a bit :) but I wonder why Pd is still about to use a relatively smaller table size. I'm curious to know how much an increase in table size actually offers a better resolution and how much it ruins performance. For instance, I'm using the same as Cyclone in ELSE oscillators, could I just reduce it at least to 8192 points or even less and down to Pd's 2048 size worry free?

Thanks
Em qua., 5 de jun. de 2024 às 13:28, Alexandre Torres Porres <porres@gmail.com> escreveu:
Nice one Matt!
Em qua., 5 de jun. de 2024 às 08:13, Christof Ressi <info@christofressi.com> escreveu:
@Miller: what do you think? IMO we should make the cos table as good as we can, so we won't have any regrets :)
+1000!!!