How to reuse built in gnark primitives with hints?

[Scratch-net]

I cannot use emulated.Element or uints because it would require rewriting it using custom gates. Is there an easier way?

[niconiconi]

they are using a customed scheme which doesn't allow us to directly integrate, we will publish a similar api for it.

[niconiconi]

@Scratch-net can you tell us more about the use case, I believe @hczphn already have a impl

[Scratch-net]

sure @niconiconi
We have several circuits in Gnark, for example this or this which we cannot compile into Expander
The only one that did compile was chachaV3 which does not use any extra hints

[hczphn]

@Scratch-net Hi, I try to compile the aes circuit and get an error message "unimplemented". This is because you use the logderivlookup api, which is not supported by ecc. Is it possible to replace it with other apis?

[Scratch-net]

Without logderivlookup it would be ~3-5 times slower, so it does not make much sense.
You can try chachaV3_oprf circuit, there are similar issues there too

[hczphn]

I guess you need to use lookup api to fasten the circuit. If so, you might try ecc logup. See if you use replace logderivlookup with that one.

[Scratch-net]

ok, what about other circuits?

[hczphn]

I tested chachaV3_oprf.
There is another error message about api.Tobinary().
In gnark, if you only provide one argument, it is ok and gnark will set the second argument to fr.Bits (the number of bits needed to represent a field element).
However, in ecc, you have to provide two argument explicitly. We should fix this issue later. Before that, you may try to rewrite the gnark repo locally and provide second argument. For example, here you should change b1 := api.ToBinary(s1) to b1 := api.ToBinary(s1, 254) since you are using BN254 field.

[hczphn]

We have created a pull request to address this issue.

In the logup check, gnark calls a commit function to compute a random value by hashing all inputs, which is computationally expensive. However, in ecc, we can directly obtain a random value. To optimize performance, we replaced the gnark commit API with our get_random_value API.

However, the random values generated by ecc cannot be used in division operations or as hint inputs. During the logup check, gnark attempts to divide the random value, which leads to a panic. To resolve this, we modified gnark accordingly.

What You Need to Do

1. Import the updated ecc version from this PR.
2. Replace the gnark repository with our fork: PolyhedraZK/gnark.
3. Modify your go.mod file to replace the gnark repository. For example, by adding the following line:
   replace github.com/consensys/gnark v0.12.0 => github.com/PolyhedraZK/gnark v0.0.0-20250304214157-c3c776fd5bf8