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------------------------------------------------------------------------------
-- --
-- GNAT RUN-TIME COMPONENTS --
-- --
-- S Y S T E M . W I D T H _ U --
-- --
-- S p e c --
-- --
-- Copyright (C) 1992-2023, Free Software Foundation, Inc. --
-- --
-- GNAT is free software; you can redistribute it and/or modify it under --
-- terms of the GNU General Public License as published by the Free Soft- --
-- ware Foundation; either version 3, or (at your option) any later ver- --
-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
-- or FITNESS FOR A PARTICULAR PURPOSE. --
-- --
-- As a special exception under Section 7 of GPL version 3, you are granted --
-- additional permissions described in the GCC Runtime Library Exception, --
-- version 3.1, as published by the Free Software Foundation. --
-- --
-- You should have received a copy of the GNU General Public License and --
-- a copy of the GCC Runtime Library Exception along with this program; --
-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
-- <http://www.gnu.org/licenses/>. --
-- --
-- GNAT was originally developed by the GNAT team at New York University. --
-- Extensive contributions were provided by Ada Core Technologies Inc. --
-- --
------------------------------------------------------------------------------
-- Preconditions in this unit are meant for analysis only, not for run-time
-- checking, so that the expected exceptions are raised. This is enforced by
-- setting the corresponding assertion policy to Ignore. Postconditions and
-- contract cases should not be executed at runtime as well, in order not to
-- slow down the execution of these functions.
pragma Assertion_Policy (Pre => Ignore,
Post => Ignore,
Contract_Cases => Ignore,
Ghost => Ignore,
Subprogram_Variant => Ignore);
-- Compute Width attribute for non-static type derived from a modular integer
-- type. The arguments Lo, Hi are the bounds of the type.
with Ada.Numerics.Big_Numbers.Big_Integers_Ghost;
generic
type Uns is mod <>;
package System.Width_U
with Pure
is
package BI_Ghost renames Ada.Numerics.Big_Numbers.Big_Integers_Ghost;
subtype Big_Integer is BI_Ghost.Big_Integer with Ghost;
subtype Big_Natural is BI_Ghost.Big_Natural with Ghost;
subtype Big_Positive is BI_Ghost.Big_Positive with Ghost;
use type BI_Ghost.Big_Integer;
package Unsigned_Conversion is
new BI_Ghost.Unsigned_Conversions (Int => Uns);
function Big (Arg : Uns) return Big_Integer renames
Unsigned_Conversion.To_Big_Integer;
Big_10 : constant Big_Integer := Big (Uns'(10)) with Ghost;
-- Maximum value of exponent for 10 that fits in Uns'Base
function Max_Log10 return Natural is
(case Uns'Base'Size is
when 8 => 2,
when 16 => 4,
when 32 => 9,
when 64 => 19,
when 128 => 38,
when others => raise Program_Error)
with Ghost;
function Width (Lo, Hi : Uns) return Natural
with
Post =>
(declare
W : constant Natural := System.Width_U.Width'Result;
begin
(if Lo > Hi then W = 0
else W > 0
and then W <= Max_Log10 + 2
and then Big (Lo) < Big_10 ** (W - 1)
and then Big (Hi) < Big_10 ** (W - 1)));
end System.Width_U;
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