```\n    uint256 timeElapsed = blockTimestamp - blockTimestampLast;\n     // overflow is desired\n    if (timeElapsed > 0 && _reserve0 != 0 && _reserve1 != 0) {\n      reserve0CumulativeLast += _reserve0 * timeElapsed;\n        reserve1CumulativeLast += _reserve1 * timeElapsed;\n     }\n```\n