unsigned integers in Ada

[rds@moss.ATT.COM]

How does one implement an unsigned integer in Ada and have a maximum
value equal to 2**(number of bits) in any given implementation?

Is this an oversight or does Ada really limit maximum integer
values to 2**(# of bits MINUS ONE)-1. More verbosely put
declaring 

     type Pointer is range 0..(2**32)-1;
     for Pointer'SIZE use 32;

is invalid for a 32 bit integer implementation because (2**32)-1
is not in the INTEGER'RANGE -(2**31)..(2**31)-1. How can I use the
leftover bit?

     subtype Pointer is INTEGER range 0..(2**32)-1;
     for Pointer'SIZE use 32;

is illegal because it is not a <first named subtype> LRM 13.1 (3)

WHAT IS A FIRST NAMED SUBTYPE?? And can someone give an example?

Any assistance will keep the hair in my head for another day (Ada problem).