I wrote a little function that has to work with big numbers
CREATE OR REPLACE FUNCTION blast_evalue(seq_len bigint, db_size bigint,
bit_score double precision)
RETURNS double precision AS $$
BEGIN
RETURN 2^(bit_score) * db_size * seq_len;
END;
$$
LANGUAGE 'plpgsql'
IMMUTABLE
RETURNS NULL ON NULL INPUT;
but it doesn't work properly unless I cast the db_size parameter when I call
the function:
select blast_evalue(273, 8903836, -55.4546);
blast_evalue
--------------
2430747228 <- wrong number. This is 273 * 8903836
(1 row)
select blast_evalue(273, 8903836::bigint, -55.4546);
blast_evalue
---------------------
4.9231356421437e-08 <- that's correct
(1 row)
I don't understand why the cast is necessary. Is there a way to make this
work without it?
Thanks
Luca
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