SYSV checksum

The SYSV checksum algorithm is a commonly used, legacy checksum algorithm. It has been implemented in UNIX System V and is also available through the GNU sum command line utility.

The manual page of the GNU sum utility program (that implements the BSD checksum algorithm) states: "sum is provided for compatibility; the cksum program is preferable in new applications."

The main part of this algorithm is simply adding up all bytes in a 32-bit sum. As a result, this algorithm has the characteristics (disadvantages and advantages) of a simple sum:

As a result, many common changes to text data are not detected by this method.

The last two lines of the algorithm reduce the total sum to a 16-bit number.

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