A cyclic redundancy check (CRC) is a type of hash function that produces a checksum (a small, fixed number of bits) against a block of data, such as a packet of network traffic or a block of a computer file. The checksum is used to detect errors after transmission or storage.
CRCs can also act as a kind of electronic fingerprint for identifying blocks of data. SWISS-PROT + TREMBL use a 64-bit Cyclic Redundancy Check for the amino acid sequences. My interest was in using CRC64 to index data in a semantic web triple store.
This implementation is influenced heavily by Python code by Gian Paolo Ciceri and crc.lisp by R. Matthew Emerson. My thanks to both these authors.