Understanding ERC-1271 - Standard Signature Validation

pragma solidity 0.8.25;

contract ERC1271 {
	// bytes4(keccak256("isValidSignature(bytes32,bytes)"))
  bytes4 constant internal MAGICVALUE = 0x1626ba7e;

  /**
   * @dev Should return whether the signature provided is valid for the provided hash
   * @param _hash      Hash of the data to be signed
   * @param _signature Signature byte array associated with _hash
   *
   * MUST return the bytes4 magic value 0x1626ba7e when function passes.
   * MUST NOT modify state (using STATICCALL for solc < 0.5, view modifier for solc > 0.5)
   * MUST allow external calls
   */
  function isValidSignature(
	  bytes32 _hash,
	  bytes memory _signature)
	  public view
	  returns (bytes4 magicValue);
}

/**
 * @notice Verifies that the signer is the owner of the signing contract.
 */
function isValidSignature(
	  bytes32 _hash,
	  bytes calldata _signature
) external override view returns (bytes4) {
		// Validate signatures
	  if (recoverSigner(_hash, _signature) == owner) {
		    return 0x1626ba7e;
	  } else {
		    return 0xffffffff;
	  }
}

/**
 * @notice Recover the signer of hash, assuming it's an EOA account
 * @dev Only for EthSign signatures
 * @param _hash       Hash of message that was signed
 * @param _signature  Signature encoded as (bytes32 r, bytes32 s, uint8 v)
 */
function recoverSigner(
	  bytes32 _hash,
	  bytes memory _signature
) internal pure returns (address signer) {
	  require(_signature.length == 65, "SignatureValidator#recoverSigner: invalid signature length");

	  // Variables are not scoped in Solidity.
	  uint8 v = uint8(_signature[64]);
	  bytes32 r = _signature.readBytes32(0);
	  bytes32 s = _signature.readBytes32(32);

	  // EIP-2 still allows signature malleability for ecrecover(). Remove this possibility and make the signature
	  // unique. Appendix F in the Ethereum Yellow paper (https://ethereum.github.io/yellowpaper/paper.pdf), defines
	  // the valid range for s in (281): 0 < s < secp256k1n ÷ 2 + 1, and for v in (282): v ∈ {27, 28}. Most
	  // signatures from current libraries generate a unique signature with an s-value in the lower half order.
	  //
	  // If your library generates malleable signatures, such as s-values in the upper range, calculate a new s-value
	  // with 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141 - s1 and flip v from 27 to 28 or
	  // vice versa. If your library also generates signatures with 0/1 for v instead 27/28, add 27 to v to accept
	  // these malleable signatures as well.
	  //
	  // Source OpenZeppelin
	  // https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/cryptography/ECDSA.sol

	  if (uint256(s) > 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0) {
	    revert("SignatureValidator#recoverSigner: invalid signature 's' value");
	  }

	  if (v != 27 && v != 28) {
	    revert("SignatureValidator#recoverSigner: invalid signature 'v' value");
	  }

	  // Recover ECDSA signer
	  signer = ecrecover(_hash, v, r, s);

	  // Prevent signer from being 0x0
	  require(
	    signer != address(0x0),
	    "SignatureValidator#recoverSigner: INVALID_SIGNER"
	  );

	  return signer;
}

function callERC1271isValidSignature(
	  address _addr,
	  bytes32 _hash,
	  bytes calldata _signature
) external view {
	  bytes4 result = IERC1271Wallet(_addr).isValidSignature(_hash, _signature);
	  require(result == 0x1626ba7e, "INVALID_SIGNATURE");
}