VerifySignature.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract VerifySignature {

    function verify(address _signer, string memory _message, bytes memory _sig)
        external pure returns (bool)
    {
        bytes32 messageHash = getMessageHash(_message);
        bytes32 ethSignedMessageHash = getEthSignedMessageHash(messageHash);

        return recover(ethSignedMessageHash, _sig) == _signer;
    }

    function getMessageHash(string memory _message) public pure returns (bytes32) {
        return keccak256(abi.encodePacked(_message));
    }

    function getEthSignedMessageHash(bytes32 _messageHash) public pure returns (bytes32) {
        return keccak256(abi.encodePacked(
            "\x19Ethereum Signed Message:\n32",
            _messageHash
        ));
    }

    function recover(bytes32 _ethSignedMessageHash, bytes memory _sig)
        public pure returns (address)
    {
        (bytes32 r, bytes32 s, uint8 v) = _split(_sig);
        
        return ecrecover(_ethSignedMessageHash, v, r, s);
    }

    function _split(bytes memory _sig) internal pure
        returns (bytes32 r, bytes32 s, uint8 v)
    {
        require(_sig.length == 65, "invalid signature length");

        assembly {
            r := mload(add(_sig, 32))
            s := mload(add(_sig, 64))
            v := byte(0, mload(add(_sig, 96)))
        }
    }
}