gistfile1.txt

function add(a, b) {
  const c = new Array(Math.max(a.length, b.length));
  const min = Math.min(a.length, b.length);
  for (let i = 0; i < min; i += 1) {
    c[i] = a[i] + b[i];
  }
  for (let i = min; i < a.length; i += 1) {
    c[i] = a[i];
  }
  for (let i = min; i < b.length; i += 1) {
    c[i] = b[i];
  }
  return c;
}

function reversalN(A, n) {
  return new Array(n - A.length).fill(0n).concat(A.slice(0).reverse());
}

LaurentSeries.prototype.multiplyMod1 = function (polynomial, precision, p) {
  const e = this.lowestDegree;
  const a = this.coefficients;
  const b = polynomial;
  if (degree(b) > degree(a)) {
    throw new RangeError();
  }
  if (degree(b) < 0) {
    return b;
  }
  // x**(e + k) >= x**-precision
  const k = 0 - precision - e;
  if (k < degree(b)) {
    throw new RangeError('inacurracy');
  }
  const a1 = reversalN(low(reversalN(a, degree(a) + 1), degree(a) + 1 - k), degree(a) + 1 - k);
  const a0 = low(a, Math.max(k, 0));
  const m1 = multiplyLow(low(a1, precision), low(b, precision), precision);
  const m2 = low(reversalN(multiplyLow(
                            low(reversalN(a0, Math.max(k, degree(a0) + 1)), degree(b)),
                            low(reversalN(b, degree(b) + 1), degree(b)),
                            degree(b)), degree(b)), precision);
  let m = add(m1, m2);
  m = mod(m, p);
  return new LaurentSeries(m, 0 - precision);
};