gcc/ada/libgnat/s-expont.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT RUN-TIME COMPONENTS                         --
   4 --                                                                          --
   5 --                        S Y S T E M . E X P O N T                         --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --          Copyright (C) 1992-2023, Free Software Foundation, Inc.         --
  10 --                                                                          --
  11 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 3,  or (at your option) any later ver- --
  14 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
  17 --                                                                          --
  18 -- As a special exception under Section 7 of GPL version 3, you are granted --
  19 -- additional permissions described in the GCC Runtime Library Exception,   --
  20 -- version 3.1, as published by the Free Software Foundation.               --
  21 --                                                                          --
  22 -- You should have received a copy of the GNU General Public License and    --
  23 -- a copy of the GCC Runtime Library Exception along with this program;     --
  24 -- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
  25 -- <http://www.gnu.org/licenses/>.                                          --
  26 --                                                                          --
  27 -- GNAT was originally developed  by the GNAT team at  New York University. --
  28 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  29 --                                                                          --
  30 ------------------------------------------------------------------------------
  31
  32 --  Signed integer exponentiation (checks on)
  33
  34 with Ada.Numerics.Big_Numbers.Big_Integers_Ghost;
  35
  36 generic
  37
  38    type Int is range <>;
  39
  40 package System.Expont
  41   with Pure, SPARK_Mode
  42 is
  43    --  Preconditions in this unit are meant for analysis only, not for run-time
  44    --  checking, so that the expected exceptions are raised. This is enforced
  45    --  by setting the corresponding assertion policy to Ignore. Postconditions
  46    --  and contract cases should not be executed at runtime as well, in order
  47    --  not to slow down the execution of these functions.
  48
  49    pragma Assertion_Policy (Pre            => Ignore,
  50                             Post           => Ignore,
  51                             Contract_Cases => Ignore,
  52                             Ghost          => Ignore);
  53
  54    package BI_Ghost renames Ada.Numerics.Big_Numbers.Big_Integers_Ghost;
  55    subtype Big_Integer is BI_Ghost.Big_Integer with Ghost;
  56    use type BI_Ghost.Big_Integer;
  57
  58    package Signed_Conversion is new BI_Ghost.Signed_Conversions (Int => Int);
  59
  60    function Big (Arg : Int) return Big_Integer is
  61      (Signed_Conversion.To_Big_Integer (Arg))
  62    with Ghost;
  63
  64    function In_Int_Range (Arg : Big_Integer) return Boolean is
  65      (BI_Ghost.In_Range (Arg, Big (Int'First), Big (Int'Last)))
  66    with Ghost;
  67
  68    function Expon (Left : Int; Right : Natural) return Int
  69    with
  70      Pre  => In_Int_Range (Big (Left) ** Right),
  71      Post => Expon'Result = Left ** Right;
  72
  73 end System.Expont;