distpi/modpow.js

// Copyright 2022 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

module.exports = (base, exponent, modulus) => {
  if (modulus === 1n) return 0n;
  let result = 1n;
  while (exponent > 0n) {
    if (exponent & 1n) {
      result = (result * base) % modulus;
    }
    exponent >>= 1n;
    base = (base * base) % modulus;
  }
  return result;
};