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+/* modarith.hpp                                
+ *
+ * Copyright (C) 2003 Sawtooth Consulting Ltd.
+ *
+ * This file is part of yaSSL.
+ *
+ * yaSSL is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * yaSSL is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
+ */
+
+
+/* based on Wei Dai's modarith.h from CryptoPP */
+
+
+#ifndef TAO_CRYPT_MODARITH_HPP
+#define TAO_CRYPT_MODARITH_HPP
+
+#include "misc.hpp"
+#include "integer.hpp"
+#include "algebra.hpp"
+
+namespace TaoCrypt {
+
+
+//! ModularArithmetic
+class ModularArithmetic : public AbstractRing<Integer>
+{
+public:
+
+    typedef int RandomizationParameter;
+    typedef Integer Element;
+
+    ModularArithmetic(const Integer &modulus = Integer::One())
+        : modulus(modulus), result((word)0, modulus.reg_.size()) {}
+
+    ModularArithmetic(const ModularArithmetic &ma)
+        : AbstractRing<Integer>(),
+        modulus(ma.modulus), result((word)0, modulus.reg_.size()) {}
+
+    const Integer& GetModulus() const {return modulus;}
+    void SetModulus(const Integer &newModulus) 
+    {   
+        modulus = newModulus;
+        result.reg_.resize(modulus.reg_.size());
+    }
+
+    virtual bool IsMontgomeryRepresentation() const {return false;}
+
+    virtual Integer ConvertIn(const Integer &a) const
+        {return a%modulus;}
+
+    virtual Integer ConvertOut(const Integer &a) const
+        {return a;}
+
+    const Integer& Half(const Integer &a) const;
+
+    bool Equal(const Integer &a, const Integer &b) const
+        {return a==b;}
+
+    const Integer& Identity() const
+        {return Integer::Zero();}
+
+    const Integer& Add(const Integer &a, const Integer &b) const;
+
+    Integer& Accumulate(Integer &a, const Integer &b) const;
+
+    const Integer& Inverse(const Integer &a) const;
+
+    const Integer& Subtract(const Integer &a, const Integer &b) const;
+
+    Integer& Reduce(Integer &a, const Integer &b) const;
+
+    const Integer& Double(const Integer &a) const
+        {return Add(a, a);}
+
+    const Integer& MultiplicativeIdentity() const
+        {return Integer::One();}
+
+    const Integer& Multiply(const Integer &a, const Integer &b) const
+        {return result1 = a*b%modulus;}
+
+    const Integer& Square(const Integer &a) const
+        {return result1 = a.Squared()%modulus;}
+
+    bool IsUnit(const Integer &a) const
+        {return Integer::Gcd(a, modulus).IsUnit();}
+
+    const Integer& MultiplicativeInverse(const Integer &a) const
+        {return result1 = a.InverseMod(modulus);}
+
+    const Integer& Divide(const Integer &a, const Integer &b) const
+        {return Multiply(a, MultiplicativeInverse(b));}
+
+    Integer CascadeExponentiate(const Integer &x, const Integer &e1,
+                                const Integer &y, const Integer &e2) const;
+
+    void SimultaneousExponentiate(Element *results, const Element &base,
+                  const Integer *exponents, unsigned int exponentsCount) const;
+
+    unsigned int MaxElementBitLength() const
+        {return (modulus-1).BitCount();}
+
+    unsigned int MaxElementByteLength() const
+        {return (modulus-1).ByteCount();}
+
+
+    static const RandomizationParameter DefaultRandomizationParameter;
+
+protected:
+    Integer modulus;
+    mutable Integer result, result1;
+
+};
+
+
+
+//! do modular arithmetics in Montgomery representation for increased speed
+class MontgomeryRepresentation : public ModularArithmetic
+{
+public:
+    MontgomeryRepresentation(const Integer &modulus);	// modulus must be odd
+
+    bool IsMontgomeryRepresentation() const {return true;}
+
+    Integer ConvertIn(const Integer &a) const
+        {return (a<<(WORD_BITS*modulus.reg_.size()))%modulus;}
+
+    Integer ConvertOut(const Integer &a) const;
+
+    const Integer& MultiplicativeIdentity() const
+     {return result1 = Integer::Power2(WORD_BITS*modulus.reg_.size())%modulus;}
+
+    const Integer& Multiply(const Integer &a, const Integer &b) const;
+
+    const Integer& Square(const Integer &a) const;
+
+    const Integer& MultiplicativeInverse(const Integer &a) const;
+
+    Integer CascadeExponentiate(const Integer &x, const Integer &e1,
+                                const Integer &y, const Integer &e2) const
+        {return AbstractRing<Integer>::CascadeExponentiate(x, e1, y, e2);}
+
+    void SimultaneousExponentiate(Element *results, const Element &base,
+            const Integer *exponents, unsigned int exponentsCount) const
+        {AbstractRing<Integer>::SimultaneousExponentiate(results, base,
+                                              exponents, exponentsCount);}
+
+private:
+    Integer u;
+    mutable AlignedWordBlock workspace;
+};
+
+
+
+
+} // namespace
+
+#endif // TAO_CRYPT_MODARITH_HPP