@polkadot/util-crypto/address/checksum.js

// Copyright 2017-2023 @polkadot/util-crypto authors & contributors
// SPDX-License-Identifier: Apache-2.0

import { sshash } from "./sshash.js";
export function checkAddressChecksum(decoded) {
  const ss58Length = decoded[0] & 0b01000000 ? 2 : 1;
  const ss58Decoded = ss58Length === 1 ? decoded[0] : (decoded[0] & 0b00111111) << 2 | decoded[1] >> 6 | (decoded[1] & 0b00111111) << 8;

  // 32/33 bytes public + 2 bytes checksum + prefix
  const isPublicKey = [34 + ss58Length, 35 + ss58Length].includes(decoded.length);
  const length = decoded.length - (isPublicKey ? 2 : 1);

  // calculate the hash and do the checksum byte checks
  const hash = sshash(decoded.subarray(0, length));
  const isValid = (decoded[0] & 0b10000000) === 0 && ![46, 47].includes(decoded[0]) && (isPublicKey ? decoded[decoded.length - 2] === hash[0] && decoded[decoded.length - 1] === hash[1] : decoded[decoded.length - 1] === hash[0]);
  return [isValid, length, ss58Length, ss58Decoded];
}