/usr/share/doc/postgresql-doc-9.3/contrib/README.pgc_checksum is in postgresql-comparator 2.2.2-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | provide fast NOT cryptographycally-secure checksum functions
for TEXT, results being of INT2, INT4 and INT8 types.
load with:
sh> psql < <path-to-postgresql>/share/contrib/pgc_checksum.sql
use as:
psql> SELECT cksum2('some text');
psql> SELECT cksum4('some text');
psql> SELECT cksum8('some text');
An empty text results in hash value 0.
A NULL value results in some predefined value.
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