djb2.sql

CREATE OR REPLACE FUNCTION djb2_hash(string text)
RETURNS bigint
IMMUTABLE 
STRICT
LANGUAGE sql
AS $$
WITH RECURSIVE t(seed, string) AS (
    VALUES (
        87049::bigint,
        $1
    )
UNION ALL
    SELECT
        (
            (
                (t.seed << 5) #
                t.seed #
                ascii (
                    substr (
                        t.string,
                        1,
                        1
                    )
                )
            )
        ),
        substr (
            t.string,
            2
        )
    FROM t
)
SELECT seed & ~(1 << 31)::bigint
FROM t
WHERE string = ''
$$;

WITH v(s, e) AS (
    VALUES
        ('foo', 796845231),
        ('bar', 796849528),
        ('disqusdev', 835117207),
        ('npr', 796837701),
        ('chicagocubs', 668901606)
), test (s,e) AS (
    SELECT s, djb2_hash(s)
    FROM v
)
SELECT * FROM test
UNION ALL
SELECT 'Total mismatched', count(*)
FROM v JOIN test ON (v.s = test.s)
WHERE test.e IS DISTINCT FROM v.e;