The pack() function is used to pack data into a binary string according to a specified format. It is commonly used in low-level data processing, network communication protocols, file format parsing, and other scenarios. To better understand and debug the binary data packed by pack(), it's often necessary to view its byte structure using tools like hexdump.

The md5_file function is used to calculate the MD5 hash value of a specified file, commonly for file integrity checks. However, sometimes even when the file path seems fine, md5_file still doesn't work, returning false or an empty value. This can be puzzling. This article will provide detailed troubleshooting steps to help you identify and resolve the issue.

The ceil() function is used to round a number up. It returns the smallest integer greater than or equal to the specified number. For example:

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