Re: Bootstrap failure on trunk: x86_64-linux-gnu

[kenner@vlsi1.ultra.nyu.edu (Richard Kenner)]

    We have a loop with the following termination code in uintp.num_bits

This sure looks like a bug in Num_Bits to me, not in the compilation
of the front-end.

The relevant code is:

   function Num_Bits (Input : Uint) return Nat is
      Bits : Nat;
      Num  : Nat;

   begin
      if UI_Is_In_Int_Range (Input) then
         Num := abs (UI_To_Int (Input));
         Bits := 0;

This code only works for one-complement machines, since it assumes a
symmetric range for Int.  It breaks when UI_To_Int returns Integer'First, as
it did in this case.  When it does, the abs produces an erroneous result
(since checking is disabled).  So it almost doesn't matter what it puts into
Num (but it actually puts in an out-of-range value there too).

Robert, what's the proper fix here?