--
-- tree_key_to_int/2
--
create or replace function tree_key_to_int(
  p_tree_key bit varying,
  p_level integer
) returns int4 as $$

-- Convert the compressed key for the node at the given level to an 
-- integer.
DECLARE
  v_level         integer default 0;
  v_parent_pos    integer default 1;
  v_pos           integer default 1;
BEGIN

  -- Find the right key first
  while v_pos < length(p_tree_key) and v_level < p_level loop
    v_parent_pos := v_pos;
    v_level := v_level + 1;
    if substring(p_tree_key, v_pos, 1) = '1' then
      v_pos := v_pos + 32;
    else
      v_pos := v_pos + 8;
    end if;
  end loop;

  if v_level < p_level then
    raise exception 'tree_key_to_int: key is at a level less than %', p_level;
  end if;

  if substring(p_tree_key, v_parent_pos, 1) = '1' then
    return substring(p_tree_key, v_parent_pos + 1, 31)::bit(31)::integer;
  else
    return substring(p_tree_key, v_parent_pos, 8)::bit(8)::integer;
  end if;

END;
$$ language plpgsql;