CRC

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

Informations

Digest sizes - 16 bits
Structure - CRC

Cryptanalysis

Re-arranging the same bytes in another order does not change the checksum.
Increasing one byte and decreasing another byte by the same amount does not change the checksum.
Adding or removing zero bytes does not change the checksum.

Pseudocode

The main part of this algorithm is simply adding up all bytes in a 32-bit sum.