Static expression fails constraint check on generated code

[jklmnn]

When a field value is used in calculations and the result is larger than the field the generated code will not compile but fail with a static constraint check.

package Test is

   type Length_Type is mod 2 ** 8;

   type Packet is
      message
         Length_1 : Length_Type;
         Length_2 : Length_Type
            then Payload
               with Size => Length_2 * 256 + Length_1
               if (Length_2 * 256 + Length_1) mod 8 = 0;
         Payload : Opaque;
      end message;

end Test;

This will lead to the following error on the generated code:

rflx-test-packet.adb:444:100: error: value not in range of type "Length_Type" defined at rflx-test.ads:16
rflx-test-packet.adb:444:100: error: static expression fails Constraint_Check