--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/ada/libgnat/s-expmod.ads	Fri Oct 27 22:46:09 2017 +0900
@@ -0,0 +1,56 @@
+------------------------------------------------------------------------------
+--                                                                          --
+--                         GNAT RUN-TIME COMPONENTS                         --
+--                                                                          --
+--                       S Y S T E M . E X P _ M O D                        --
+--                                                                          --
+--                                 S p e c                                  --
+--                                                                          --
+--           Copyright (C) 1992-2017, 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.      --
+--                                                                          --
+------------------------------------------------------------------------------
+
+--  This function performs exponentiation of a modular type with nonbinary
+--  modulus values. Arithmetic is done in Long_Long_Unsigned, with explicit
+--  accounting for the modulus value which is passed as the second argument.
+--  Note that 1 is a binary modulus (2**0), so the compiler should not (and
+--  will not) call this function with Modulus equal to 1.
+
+with System.Unsigned_Types;
+
+package System.Exp_Mod is
+   pragma Pure;
+   use type System.Unsigned_Types.Unsigned;
+
+   subtype Power_Of_2 is System.Unsigned_Types.Unsigned with
+     Dynamic_Predicate =>
+        Power_Of_2 /= 0 and then (Power_Of_2 and (Power_Of_2 - 1)) = 0;
+
+   function Exp_Modular
+     (Left    : System.Unsigned_Types.Unsigned;
+      Modulus : System.Unsigned_Types.Unsigned;
+      Right   : Natural) return System.Unsigned_Types.Unsigned
+   with
+       Pre  => Modulus /= 0 and then Modulus not in Power_Of_2,
+       Post => Exp_Modular'Result = Left ** Right mod Modulus;
+
+end System.Exp_Mod;