1const bn128 = require("snarkjs").bn128;
  2const bigInt = require("snarkjs").bigInt;
  3
  4exports.addPoint = addPoint;
  5exports.mulPointEscalar = mulPointEscalar;
  6exports.inCurve = inCurve;
  7exports.inSubgroup = inSubgroup;
  8exports.packPoint = packPoint;
  9exports.unpackPoint = unpackPoint;
 10exports.Base8 = [
 11    bigInt("17777552123799933955779906779655732241715742912184938656739573121738514868268"),
 12    bigInt("2626589144620713026669568689430873010625803728049924121243784502389097019475")
 13];
 14exports.order = bigInt("21888242871839275222246405745257275088614511777268538073601725287587578984328");
 15exports.subOrder = exports.order.shr(3);
 16exports.p = bn128.r;
 17
 18
 19function addPoint(a,b) {
 20    const q = bn128.r;
 21    const cta = bigInt("168700");
 22    const d = bigInt("168696");
 23
 24    const res = [];
 25    res[0] = bigInt((a[0]*b[1] + b[0]*a[1]) *  bigInt(bigInt("1") + d*a[0]*b[0]*a[1]*b[1]).inverse(q)).affine(q);
 26    res[1] = bigInt((a[1]*b[1] - cta*a[0]*b[0]) * bigInt(bigInt("1") - d*a[0]*b[0]*a[1]*b[1]).inverse(q)).affine(q);
 27    return res;
 28}
 29
 30function mulPointEscalar(base, e) {
 31    let res = [bigInt("0"),bigInt("1")];
 32    let rem = bigInt(e);
 33    let exp = base;
 34
 35    while (! rem.isZero()) {
 36        if (rem.isOdd()) {
 37            res = addPoint(res, exp);
 38        }
 39        exp = addPoint(exp, exp);
 40        rem = rem.shr(1);
 41    }
 42
 43    return res;
 44}
 45
 46function inSubgroup(P) {
 47    if (!inCurve(P)) return false;
 48    const res= mulPointEscalar(P, exports.subOrder);
 49    return (res[0].equals(bigInt(0))) && (res[1].equals(bigInt(1)));
 50}
 51
 52function inCurve(P) {
 53    const F = bn128.Fr;
 54
 55    const a = bigInt("168700");
 56    const d = bigInt("168696");
 57
 58    const x2 = F.square(P[0]);
 59    const y2 = F.square(P[1]);
 60
 61    if (!F.equals(
 62        F.add(F.mul(a, x2), y2),
 63        F.add(F.one, F.mul(F.mul(x2, y2), d)))) return false;
 64
 65    return true;
 66}
 67
 68function packPoint(P) {
 69    const buff = bigInt.leInt2Buff(P[1], 32);
 70    if (P[0].greater(exports.p.shr(1))) {
 71        buff[31] = buff[31] | 0x80;
 72    }
 73    return buff;
 74}
 75
 76function unpackPoint(_buff) {
 77    const F = bn128.Fr;
 78
 79    const buff = Buffer.from(_buff);
 80    let sign = false;
 81    const P = new Array(2);
 82    if (buff[31] & 0x80) {
 83        sign = true;
 84        buff[31] = buff[31] & 0x7F;
 85    }
 86    P[1] = bigInt.leBuff2int(buff);
 87    if (P[1].greaterOrEquals(exports.p)) return null;
 88
 89    const a = bigInt("168700");
 90    const d = bigInt("168696");
 91
 92    const y2 = F.square(P[1]);
 93
 94    let x = F.sqrt(F.div(
 95        F.sub(F.one, y2),
 96        F.sub(a, F.mul(d, y2))));
 97
 98    if (x == null) return null;
 99
100    if (sign) x = F.neg(x);
101
102    P[0] = F.affine(x);
103
104    return P;
105}