57 lines
3.3 KiB
Ada
57 lines
3.3 KiB
Ada
------------------------------------------------------------------------------
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-- --
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-- GNAT RUN-TIME COMPONENTS --
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-- --
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-- S Y S T E M . E X P _ M O D --
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-- --
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-- S p e c --
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-- --
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-- Copyright (C) 1992-2015, Free Software Foundation, Inc. --
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-- --
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-- GNAT is free software; you can redistribute it and/or modify it under --
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-- terms of the GNU General Public License as published by the Free Soft- --
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-- ware Foundation; either version 3, or (at your option) any later ver- --
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-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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-- or FITNESS FOR A PARTICULAR PURPOSE. --
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-- --
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-- As a special exception under Section 7 of GPL version 3, you are granted --
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-- additional permissions described in the GCC Runtime Library Exception, --
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-- version 3.1, as published by the Free Software Foundation. --
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-- --
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-- You should have received a copy of the GNU General Public License and --
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-- a copy of the GCC Runtime Library Exception along with this program; --
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-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
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-- <http://www.gnu.org/licenses/>. --
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-- --
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-- GNAT was originally developed by the GNAT team at New York University. --
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-- Extensive contributions were provided by Ada Core Technologies Inc. --
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-- --
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------------------------------------------------------------------------------
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-- This function performs exponentiation of a modular type with nonbinary
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-- modulus values. Arithmetic is done in Long_Long_Unsigned, with explicit
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-- accounting for the modulus value which is passed as the second argument.
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-- Note that 1 is a binary modulus (2**0), so the compiler should not (and
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-- will not) call this function with Modulus equal to 1.
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with System.Unsigned_Types;
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package System.Exp_Mod is
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pragma Pure;
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use type System.Unsigned_Types.Unsigned;
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subtype Power_Of_2 is System.Unsigned_Types.Unsigned with
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Dynamic_Predicate =>
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Power_Of_2 /= 0 and then (Power_Of_2 and (Power_Of_2 - 1)) = 0;
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function Exp_Modular
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(Left : System.Unsigned_Types.Unsigned;
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Modulus : System.Unsigned_Types.Unsigned;
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Right : Natural) return System.Unsigned_Types.Unsigned
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with
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Pre => Modulus /= 0 and then Modulus not in Power_Of_2,
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Post => Exp_Modular'Result = Left ** Right mod Modulus;
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end System.Exp_Mod;
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