Postgresql ERROR: operator does not exist: bigint << bigint - postgresql

Question

My algorithm was working fine but with a new big database, my integers variable exceed the max limit size. (I use the powerset algorithm : https://www.postgresql.org/message-id/20060924054759.GA71934%40winnie.fuhr.org)
So I've decided to change all of my integer to bigint, but now I have a problem on the comparison operator... I don't know how to manage it :
CREATE OR REPLACE FUNCTION powerset(a anyarray)
RETURNS SETOF anyarray AS
$BODY$
DECLARE
retval a%TYPE;
alower bigint := array_lower(a, 1);
aupper bigint := array_upper(a, 1);
j bigint;
k bigint;
BEGIN
FOR i IN 1 .. COALESCE((CAST(1 AS BIGINT) << (aupper - alower + 1)) - 1, 0) LOOP
retval := '{}';
j := alower;
k := i;
WHILE k > CAST(0 AS BIGINT) LOOP
IF k & CAST(1 AS BIGINT) = CAST(1 AS BIGINT) THEN
retval := array_append(retval, a[j]);
END IF;
j := j + CAST(1 AS BIGINT);
k := k >> CAST(1 AS BIGINT);
END LOOP;
RETURN NEXT retval;
END LOOP;
RETURN;
END;
$BODY$
LANGUAGE plpgsql IMMUTABLE STRICT
COST 100
ROWS 1000;
ALTER FUNCTION powerset(anyarray)
OWNER TO postgres;
I've got the error on line :
FOR i IN 1 .. COALESCE((CAST(1 AS BIGINT) << (aupper - alower + 1)) - 1, 0) LOOP
Error 42883
Postgresql ERROR: operator does not exist: bigint << bigint

Answer 1

The type of the right operand of bitwise shift operators is integer. Unfortunately, this is not mentioned in the documentation.
You should cast the right operand of shift operators to integer:
-- instead of
-- COALESCE((CAST(1 AS BIGINT) << (aupper - alower + 1)) - 1, 0)
-- use
select COALESCE(1 << (aupper - alower + 1)::int- 1, 0)::bigint
-- instead of
-- k := k >> CAST(1 AS BIGINT);
--- use
k := k >> 1;
-- etc
You can check possible types of operands by querying the system catalog pg_operator, e.g.:
select oprname, oprleft::regtype, oprright::regtype
from pg_operator
where oprname = '<<'
and oprcode::text like '%shl%' -- shift left functions
oprname | oprleft | oprright
---------+----------+----------
<< | smallint | integer
<< | integer | integer
<< | bigint | integer
(3 rows)
The above result shows that left operand of the operator << (bitwise shift left) can be smallint, integer or bigint and right operand must be integer.