fast_pedersen_hash.ts

// NOTE: it's experimental.
// https://gist.github.com/sc0Vu/09e7f1838785825de800cd3422e4511a
// https://github.com/paulmillr/scure-starknet/blob/main/index.ts

const PEDERSEN_POINTS = [
    new ProjectivePoint(2089986280348253421170679821480865132823066470938446095505822317253594081284n, 1713931329540660377023406109199410414810705867260802078187082345529207694986n, 1n),
    new ProjectivePoint(996781205833008774514500082376783249102396023663454813447423147977397232763n, 1668503676786377725805489344771023921079126552019160156920634619255970485781n, 1n),
    new ProjectivePoint(2251563274489750535117886426533222435294046428347329203627021249169616184184n, 1798716007562728905295480679789526322175868328062420237419143593021674992973n, 1n),
    new ProjectivePoint(2138414695194151160943305727036575959195309218611738193261179310511854807447n, 113410276730064486255102093846540133784865286929052426931474106396135072156n, 1n),
    new ProjectivePoint(2379962749567351885752724891227938183011949129833673362440656643086021394946n, 776496453633298175483985398648758586525933812536653089401905292063708816422n, 1n),
];

function pedersenSingle(value, p1, p2) {
    let x = pedersenArg(value);
    if (
        x < 0 ||
        x >= BigInt(3618502788666131213697322783095070105623107215331596699973092056135872020481)
    ) throw new Error('invalid value');
    const highNibble = x >> 248n;
    const lowPart = x & (2n ** 248n - 1n);
    return p1.multiplyUnsafe(lowPart).add(p2.multiplyUnsafe(highNibble));
}

// shift_point + x_low * P_0 + x_high * P1 + y_low * P2  + y_high * P3
export function pedersen(x, y) {
    let point = PEDERSEN_POINTS[0];
    point = point.add(pedersenSingle(x, PEDERSEN_POINTS[1], PEDERSEN_POINTS[2]))
    point = point.add(pedersenSingle(y, PEDERSEN_POINTS[3], PEDERSEN_POINTS[4]))
    return extractX(point.toRawBytes(true));
}