Перевод строки содержащей число в шестнадцатеричной системе в обычное целое число

CONVERT('FF') - 255

CONVERT('0110',2) - 6

CREATE FUNCTION digit(d text) RETURNS INTEGER
AS $$
SELECT ascii(d) - CASE
        WHEN d BETWEEN '0' AND '9' THEN ascii('0')
        ELSE ascii('A') - 10
    END;
$$ IMMUTABLE LANGUAGE SQL;
 
CREATE FUNCTION CONVERT(num text, radix INTEGER DEFAULT 16)
RETURNS INTEGER
AS $$
WITH s(d,ord) AS (
    SELECT *
    FROM regexp_split_to_table(reverse(UPPER(num)),'') WITH ORDINALITY
)
SELECT SUM(digit(d) * radix^(ord-1))::INTEGER
FROM s;
$$ IMMUTABLE LANGUAGE SQL;

CREATE FUNCTION digit(d text) RETURNS INTEGER
AS $$
SELECT ascii(d) - CASE
        WHEN d BETWEEN '0' AND '9' THEN ascii('0')
        ELSE ascii('A') - 10
    END;
$$ IMMUTABLE LANGUAGE SQL;
 
CREATE FUNCTION CONVERT(hex text) RETURNS INTEGER
AS $$
WITH s(d,ord) AS (
    SELECT *
    FROM regexp_split_to_table(reverse(UPPER(hex)),'') WITH ORDINALITY
)
SELECT SUM(digit(d) * 16^(ord-1))::INTEGER
FROM s;
$$ IMMUTABLE LANGUAGE SQL;