fibonacci.sql

-- Super fast quasi fibonacci function for postgresql

-- Returns rounded big integer
CREATE OR REPLACE FUNCTION fib (
    n integer
) RETURNS bigint AS $$
BEGIN
    IF n > 91 THEN
        RAISE EXCEPTION 'Bigint overflow past fib(91) [%]', n;
    END IF;
    RETURN (1.618^n)/ (|/ 2);
END;
$$ LANGUAGE plpgsql;

-- Returns double precission number
CREATE OR REPLACE FUNCTION fib (
    n integer
) RETURNS double precision AS $$
BEGIN
    IF n > 1475 THEN
        RAISE EXCEPTION 'Double precision overflow past fib(1475) [%]', n;
    END IF;
    RETURN (1.618^n)/ (|/ 2);
END;
$$ LANGUAGE plpgsql;