library Strings {
 bytes16 private constant _HEX_SYMBOLS = "0123456789abcdef";

 /**
 * @dev Converts a `uint256` to its ASCII `string` decimal representation.
 */
 function toString(uint256 value) internal pure returns (string memory) {
 // Inspired by OraclizeAPI's implementation - MIT licence
 // https://github.com/oraclize/ethereum-api/blob/b42146b063c7d6ee1358846c198246239e9360e8/oraclizeAPI_0.4.25.sol

 if (value == 0) {
 return "0";
 }
 uint256 temp = value;
 uint256 digits;
 while (temp != 0) {
 digits++;
 temp /= 10;
 }
 bytes memory buffer = new bytes(digits);
 while (value != 0) {
 digits -= 1;
 buffer[digits] = bytes1(uint8(48 + uint256(value % 10)));
 value /= 10;
 }
 return string(buffer);
 }

 /**
 * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation.
 */
 function toHexString(uint256 value) internal pure returns (string memory) {
 if (value == 0) {
 return "0x00";
 }
 uint256 temp = value;
 uint256 length = 0;
 while (temp != 0) {
 length++;
 temp >>= 8;
 }
 return toHexString(value, length);
 }

 /**
 * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation with fixed length.
 */
 function toHexString(uint256 value, uint256 length) internal pure returns (string memory) {
 bytes memory buffer = new bytes(2 * length + 2);
 buffer[0] = "0";
 buffer[1] = "x";
 for (uint256 i = 2 * length + 1; i > 1; --i) {
 buffer[i] = _HEX_SYMBOLS[value & 0xf];
 value >>= 4;
 }
 require(value == 0, "Strings: hex length insufficient");
 return string(buffer);
 }
}
/**
 * @dev String operations.
 */
function toHexString(uint256 value, uint256 length) internal pure returns (string memory) {
bytes memory buffer = new bytes(2 * length + 2);
buffer[0] = "0";
buffer[1] = "x";
for (uint256 i = 2 * length + 1; i > 1; --i) {
buffer[i] = _HEX_SYMBOLS[value & 0xf];
value >>= 4;
}
require(value == 0, "Strings: hex length insufficient");
return string(buffer);
}

/**
 * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation with fixed length.
 */