Poseidon Solidity and JS produce different outputs given the same inputs

[Arinerron]

In circomlibjs version 0.1.7, the generated Solidity code and JS functions for poseidon produce a different hash for the same input. Hardhat running with solc version 0.8.27 if that matters.

    async initialize() {
        // deploy hash contracts

        let poseidon2Factory = new ethers.ContractFactory(
            poseidonContract.generateABI(2),
            poseidonContract.createCode(2),
            this.owner
        );
        this.poseidon2 = await poseidon2Factory.deploy();


        // test it
        
        let onchainP2Result = ethers.toBigInt(await this.poseidon2['poseidon(uint256[2])']([1, 2]));
        let offchainP2Result = ethers.toBigInt((await buildPoseidon(2))([1, 2]));
        if (onchainP2Result !== offchainP2Result) {
            console.log(onchainP2Result, offchainP2Result);
            throw new Error('Poseidon2 test failed', {onchainP2Result, offchainP2Result});
        }
    }

I saw issue #13, but:

• it's talking about circom vs JS (not Solidity vs JS)
• for that bug, it seems to be outputting the same hashes, just with different return types. For this bug, the functions output entirely different bytes.

Please let me know if you need any help reproducing this. I actually can't get the two implementations to output the same hash at all.

[Arinerron]

Also tested with circomlibjs 0.1.6. Same result.

poseidon2 of [1, 2] is (bigint):

• onchain (Solidity): 7853200120776062878684798364095072458815029376092732009249414926327459813530n
• offchain (JS): 53742210201261010786651533977371650068498129444170938640721811794703579322377n

[Arinerron]

It was a pain adapting the code, but downgrading to 0.0.8 worked for me. Here's my hacky code to temporarily adapt interfaces from 0.1.7 to 0.0.8.

Replace this:

const { buildPoseidon, buildMimcSponge } = require('circomlibjs');

With this:

const {
    poseidon_gencontract,
    mimcsponge_gencontract,
    poseidon,
    mimcsponge
} = require('circomlibjs');
let poseidonContract = poseidon_gencontract;
let mimcSpongecontract = mimcsponge_gencontract;
let buildPoseidon = async (nRounds) => {
    return poseidon;
}
let buildMimcSponge = async (nRounds, seed) => {
    return mimcsponge;
}
const Scalar = require("ffjavascript").Scalar
const ZqField = require("ffjavascript").ZqField;
const F = new ZqField(Scalar.fromString("21888242871839275222246405745257275088548364400416034343698204186575808495617"));
mimcsponge.F = F;

[OBrezhniev]

Take a look at poseidon contract tests to see an example of getting and comparing results from js and contract.