CREATE OR REPLACE FUNCTION mergesort(A double precision[], p integer, r integer)
RETURNS double precision[] AS $$
    SELECT
        CASE WHEN p < r THEN mergesort(A,p,floor((p+r)/2)::integer)
             WHEN p < r THEN mergesort(A,floor((p+r)/2)::integer+1,r)
             WHEN p < r THEN merge(A,p,floor((p+r)/2)::integer,r)
             ELSE A
    END;
$$ LANGUAGE SQL;

CREATE FUNCTION merge(A double precision[], p integer, q integer, r integer)
RETURNS double precision[] AS $$
DECLARE
 n1 integer := q-p+1;
 n2 integer := r-q;
 L double precision[];
 Ri double precision[];
 g integer;
 h integer;
BEGIN
 L = ARRAY[n1+1];
 Ri = ARRAY[n2+1];
 FOR i in 1..(n1+1) LOOP
    L[i] = A[p+i-1];
 END LOOP;
 FOR j in 1..n2+1 LOOP
    Ri[j] = A[q+j];
 END LOOP;
 L[n1+1] = 'Infinity';
 Ri[n2+1] = 'Infinity';
 g = 1;
 h = 1;
 FOR k in p..r LOOP
    IF L[g] <= Ri[h] THEN
        A[k] = L[g];
        g = g + 1;
    ELSE
        A[k] = Ri[h];
        h = h + 1;
    END IF;
 END LOOP;
 RETURN A;
END;
$$ LANGUAGE plpgsql;