@kotevode/ffjavascript/src/futils.js

Finite Field Library in Javascript

/*
    Copyright 2018 0kims association.

    This file is part of snarkjs.

    snarkjs is a free software: you can redistribute it and/or
    modify it under the terms of the GNU General Public License as published by the
    Free Software Foundation, either version 3 of the License, or (at your option)
    any later version.

    snarkjs is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
    or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
    more details.

    You should have received a copy of the GNU General Public License along with
    snarkjs. If not, see <https://www.gnu.org/licenses/>.
*/

import * as Scalar from "./scalar.js";


export function mulScalar(F, base, e) {
    let res;

    if (Scalar.isZero(e)) return F.zero;

    const n = Scalar.naf(e);

    if (n[n.length-1] == 1) {
        res = base;
    } else if (n[n.length-1] == -1) {
        res = F.neg(base);
    } else {
        throw new Error("invlaud NAF");
    }

    for (let i=n.length-2; i>=0; i--) {

        res = F.double(res);

        if (n[i] == 1) {
            res = F.add(res, base);
        } else if (n[i] == -1) {
            res = F.sub(res, base);
        }
    }

    return res;
}


/*
exports.mulScalar = (F, base, e) =>{
    let res = F.zero;
    let rem = bigInt(e);
    let exp = base;

    while (! rem.eq(bigInt.zero)) {
        if (rem.and(bigInt.one).eq(bigInt.one)) {
            res = F.add(res, exp);
        }
        exp = F.double(exp);
        rem = rem.shiftRight(1);
    }

    return res;
};
*/


export function exp(F, base, e) {

    if (Scalar.isZero(e)) return F.one;

    const n = Scalar.bits(e);

    if (n.length==0) return F.one;

    let res = base;

    for (let i=n.length-2; i>=0; i--) {

        res = F.square(res);

        if (n[i]) {
            res = F.mul(res, base);
        }
    }

    return res;
}