```\n/// @notice Implements bitcoin's hash256 (double sha2)\n/// @dev abi.encodePacked changes the return to bytes instead of bytes32\n/// @param \_b The pre-image\n/// @return The digest\nfunction hash256(bytes memory \_b) internal pure returns (bytes32) {\n    return abi.encodePacked(sha256(abi.encodePacked(sha256(\_b)))).toBytes32();\n}\n```\n