library ECRecovery {
  /**
   * @dev Recover signer address from a personal signed message by using his signature
   * @param hash bytes32 message, the hash is the signed message. What is recovered is the signer address.
   * @param sig bytes signature, the signature is generated using web3.personal.sign()
   */
  function personalRecover(bytes32 hash, bytes sig) internal pure returns (address) {
    return recover(toEthSignedMessageHash(hash), sig);
  }

  /**
   * @dev Recover signer address from a message by using his signature
   * @param hash bytes32 message, the hash is the signed message. What is recovered is the signer address.
   * @param sig bytes signature, the signature is generated using web3.eth.sign()
   */
  function recover(bytes32 hash, bytes sig) internal pure returns (address) {
    bytes32 r;
    bytes32 s;
    uint8 v;

    //Check the signature length
    if (sig.length != 65) {
      return (address(0));
    }

    // Divide the signature in r, s and v variables
    assembly {
      r := mload(add(sig, 32))
      s := mload(add(sig, 64))
      v := byte(0, mload(add(sig, 96)))
    }

    // Version of signature should be 27 or 28, but 0 and 1 are also possible versions
    if (v < 27) {
      v += 27;
    }

    // If the version is correct return the signer address
    if (v != 27 && v != 28) {
      return (address(0));
    } else {
      return ecrecover(hash, v, r, s);
    }
  }

  /**
   * toEthSignedMessageHash
   * @dev prefix a bytes32 value with "\x19Ethereum Signed Message:"
   * @dev and hash the result
   */
  function toEthSignedMessageHash(bytes32 hash)
    internal
    pure
    returns (bytes32)
  {
    // 32 is the length in bytes of hash,
    // enforced by the type signature above
    return keccak256(abi.encodePacked(
      "\x19Ethereum Signed Message:\n32",
      hash
    ));
  }
}
// Using ECRecovery from open-zeppelin@ad12381549c4c0711c2f3310e9fb1f65d51c299c + added personalRecover function
// See https://github.com/OpenZeppelin/openzeppelin-solidity/blob/ad12381549c4c0711c2f3310e9fb1f65d51c299c/contracts/ECRecovery.sol
function personalRecover(bytes32 hash, bytes sig) internal pure returns (address) {
    return recover(toEthSignedMessageHash(hash), sig);
  }
/**
 * @dev Recover signer address from a personal signed message by using his signature
 * @param hash bytes32 message, the hash is the signed message. What is recovered is the signer address.
 * @param sig bytes signature, the signature is generated using web3.personal.sign()
 */