------------------------------ Commands Entered ------------------------------
CREATE OR REPLACE FUNCTION
bits
( in_number SMALLINT )
  RETURNS CHAR(16)
  LANGUAGE SQL
  DETERMINISTIC
  NO EXTERNAL ACTION
RETURN
SELECT LISTAGG(
          SUBSTR(
             '...0000000100100011010001010110011110001001101010111100110111101111'
           , LOCATE( SUBSTR(HEX(in_number) , k , 1) , '0123456789ABCDEF' ) * 4
           , 4
          )
       ) WITHIN GROUP (
          ORDER BY SUBSTR( HEX(INT(1)) , 2 , 1 ) -- IF   little endian,
                   * ( (k - 1) / 2 ) DESC        -- THEN reverse byte(= two hex digits) order.
                 , k
       )
 FROM  (VALUES 1 , 2 , 3 , 4) k(k)
;
------------------------------------------------------------------------------
DB20000I  The SQL command completed successfully.

------------------------------ Commands Entered ------------------------------
WITH
 test_data(in_number) AS (
SELECT SMALLINT(in_number)
 FROM  (VALUES
          ( 32767) , ( 16383)
        , (  4096) , (   118)
        , (    63) , (    16)
        , (     2) , (     1)
        , (     0) , (    -1)
        , (    -2) , (    -3)
        , (   -64) , (-32768)
       ) in(in_number)
)
SELECT in_number
     , HEX(in_number)  AS hex
     , BITS(in_number) AS bits
 FROM  test_data
;
------------------------------------------------------------------------------

IN_NUMBER HEX  BITS            
--------- ---- ----------------
    32767 FF7F 0111111111111111
    16383 FF3F 0011111111111111
     4096 0010 0001000000000000
      118 7600 0000000001110110
       63 3F00 0000000000111111
       16 1000 0000000000010000
        2 0200 0000000000000010
        1 0100 0000000000000001
        0 0000 0000000000000000
       -1 FFFF 1111111111111111
       -2 FEFF 1111111111111110
       -3 FDFF 1111111111111101
      -64 C0FF 1111111111000000
   -32768 0080 1000000000000000

  14 record(s) selected.