Fun fact GNAT (GCC Ada front-end) will use a biased representation for range type when packing tight:

  with Ada.Text_IO; use Ada.Text_IO;
  procedure T is
   type T1 is range 16..19;
   type T2 is range -7..0;
   type R is record
      A : T1;
      B,C : T2;
   end record;
   for  R use
    record
       A at 0 range  0 .. 1;
       B at 0 range  2 .. 4;
       C at 0 range  5 .. 7;
    end record;
   X : R := (17,-2,-3);
  begin
   Put_Line(X'Size'Image); -- 8 bits
  end T;