Enable GLV optimization?

[oleiba]

Now that U.S. Patent No. 7,110,538 has expired, the endomorphism optimization for point multiplication can be enabled by default. Also, it is already implemented in libsecp256k1 but was just turned off by default.
Is it already supported with this crate, or expected to be supported with a future release?

[real-or-random]

upstream will just remove the non-endo code, so we'll get this automatically with the first update afterwards: bitcoin-core/secp256k1#826

[oleiba]

Great.
So just to make sure I got it right: there is no need for another release because the git clone https://github.com/bitcoin-core/secp256k1.git takes the HEAD by default, correct?
For a library using this crate, it would simply require doing a cargo build?

[real-or-random]

No, we need a release. We have a copy of secp256k1 in our repo. When we update the copy, we will bump secp256k1-sys, see #229 for a past example. I think we want to do this as soon as bitcoin-core/secp256k1#826 is merged.

[oleiba]

OK, makes sense. I will follow for the upcoming release.
BTW, I think this would also allow deleting the endomorphism feature, as it would always be turned on.

[elichai]

@oleiba for now feel free to enable the feature for your crates,
as @real-or-random we'll probably wait for bitcoin-core/secp256k1#826 to be merged and maybe even safeGCD before we will update upstream here and remove the feature

[apoelstra]

I think we should leave this open as a tracking issue for "GLV by default".

It's also worth considering us turning on the feature by default, which we can do in a minor release.

[elichai]

I think this is done since e687622

This is done from secp256k1 version 0.20.0 and up.