#ifndef ALGEBRA_H
#define ALGEBRA_H

class Integer;

template <class T> class AbstractGroup
{
public:
	typedef T Element;

	virtual ~AbstractGroup() {}

	virtual bool Equal(const Element &a, const Element &b) const =0;
	virtual Element Zero() const =0;
	virtual Element Add(const Element &a, const Element &b) const =0;
	virtual Element Inverse(const Element &a) const =0;

	virtual Element Double(const Element &a) const;
	virtual Element Subtract(const Element &a, const Element &b) const;
	virtual Element& Accumulate(Element &a, const Element &b) const;
	virtual Element& Reduce(Element &a, const Element &b) const;

	virtual Element IntMultiply(const Element &a, const Integer &e) const;
	virtual Element CascadeIntMultiply(const Element &x, const Integer &e1, const Element &y, const Integer &e2) const;
};

template <class T> class AbstractRing : public AbstractGroup<T>
{
public:
	typedef T Element;

	virtual bool IsUnit(const Element &a) const =0;
	virtual Element One() const =0;
	virtual Element Multiply(const Element &a, const Element &b) const =0;
	virtual Element MultiplicativeInverse(const Element &a) const =0;

	virtual Element Square(const Element &a) const;
	virtual Element Divide(const Element &a, const Element &b) const;

	virtual Element Exponentiate(const Element &a, const Integer &e) const;
	virtual Element CascadeExponentiate(const Element &x, const Integer &e1, const Element &y, const Integer &e2) const;
};

// ********************************************************

// VC50 workaround: no member template support yet
template <class Element, class Iterator> Element GeneralCascadeMultiplication(const AbstractGroup<Element> &group, Iterator begin, Iterator end);
#if defined(BREAK_GCC34)
template <class Element, class Iterator> Element GeneralCascadeExponentiation(const AbstractRing<Element> &ring, Iterator begin, Iterator end);
#endif /* BREAK_GCC34 */

// ********************************************************

template <class T> class AbstractField : public AbstractRing<T>
{
public:
	bool IsUnit(const typename T::Element &a) const
		{return !Equal(a, this->Zero());}
};

template <class T> class AbstractEuclideanDomain : public AbstractRing<T>
{
public:
	typedef T Element;

	virtual void DivisionAlgorithm(Element &r, Element &q, const Element &a, const Element &d) const =0;

	virtual Element Mod(const Element &a, const Element &b) const;
	virtual Element Gcd(const Element &a, const Element &b) const;
};

// ********************************************************

template <class T> class MultiplicativeGroup : public AbstractGroup<typename T::Element>
{
public:
	typedef T Ring;

	MultiplicativeGroup(const Ring &m_ring)
		: m_ring(m_ring) {}

	const Ring & GetRing() const
		{return m_ring;}

	bool Equal(const typename T::Element &a, const typename T::Element &b) const
		{return m_ring.Equal(a, b);}

	typename T::Element Zero() const
		{return m_ring.One();}

	typename T::Element Add(const typename T::Element &a, const typename T::Element &b) const
		{return m_ring.Multiply(a, b);}

	typename T::Element& Accumulate(typename T::Element &a, const typename T::Element &b) const
		{return a = m_ring.Multiply(a, b);}

	typename T::Element Inverse(const typename T::Element &a) const
		{return m_ring.MultiplicativeInverse(a);}

	typename T::Element Subtract(const typename T::Element &a, const typename T::Element &b) const
		{return m_ring.Divide(a, b);}

	typename T::Element& Reduce(typename T::Element &a, const typename T::Element &b) const
		{return a = m_ring.Divide(a, b);}

	typename T::Element Double(const typename T::Element &a) const
		{return m_ring.Square(a);}

protected:
	const Ring &m_ring;
};

template <class T> class EuclideanDomainOf : public AbstractEuclideanDomain<T>
{
public:
	typedef T Element;

	EuclideanDomainOf() {}

	bool Equal(const Element &a, const Element &b) const
		{return a==b;}

	Element Zero() const
		{return Element::Zero();}

	Element Add(const Element &a, const Element &b) const
		{return a+b;}

	Element& Accumulate(Element &a, const Element &b) const
		{return a+=b;}

	Element Inverse(const Element &a) const
		{return -a;}

	Element Subtract(const Element &a, const Element &b) const
		{return a-b;}

	Element& Reduce(Element &a, const Element &b) const
		{return a-=b;}

	Element Double(const Element &a) const
		{return a.Doubled();}

	Element One() const
		{return Element::One();}

	Element Multiply(const Element &a, const Element &b) const
		{return a*b;}

	Element Square(const Element &a) const
		{return a.Squared();}

	bool IsUnit(const Element &a) const
		{return a.IsUnit();}

	Element MultiplicativeInverse(const Element &a) const
		{return a.MultiplicativeInverse();}

	Element Divide(const Element &a, const Element &b) const
		{return a/b;}

	Element Mod(const Element &a, const Element &b) const
		{return a%b;}

	void DivisionAlgorithm(Element &r, Element &q, const Element &a, const Element &d) const
		{Element::Divide(r, q, a, d);}
};

template <class T> class QuotientRing : public AbstractRing<typename T::Element>
{
public:
	typedef T EuclideanDomain;

	QuotientRing(const EuclideanDomain &domain, const typename T::Element &modulus)
		: m_domain(domain), m_modulus(modulus) {}

	const EuclideanDomain & GetDomain() const
		{return m_domain;}

	const typename T::Element & GetModulus() const
		{return m_modulus;}

	bool Equal(const typename T::Element &a, const typename T::Element &b) const
		{return m_domain.Equal(m_domain.Mod(m_domain.Subtract(a, b), m_modulus), m_domain.Zero());}

	typename T::Element Zero() const
		{return m_domain.Zero();}

	typename T::Element Add(const typename T::Element &a, const typename T::Element &b) const
		{return m_domain.Add(a, b);}

	typename T::Element& Accumulate(typename T::Element &a, const typename T::Element &b) const
		{return m_domain.Accumulate(a, b);}

	typename T::Element Inverse(const typename T::Element &a) const
		{return m_domain.Inverse(a);}

	typename T::Element Subtract(const typename T::Element &a, const typename T::Element &b) const
		{return m_domain.Subtract(a, b);}

	typename T::Element& Reduce(typename T::Element &a, const typename T::Element &b) const
		{return m_domain.Reduce(a, b);}

	typename T::Element Double(const typename T::Element &a) const
		{return m_domain.Double(a);}

	bool IsUnit(const typename T::Element &a) const
		{return m_domain.IsUnit(m_domain.Gcd(a, m_modulus));}

	typename T::Element One() const
		{return m_domain.One();}

	typename T::Element Multiply(const typename T::Element &a, const typename T::Element &b) const
		{return m_domain.Mod(m_domain.Multiply(a, b), m_modulus);}

	typename T::Element Square(const typename T::Element &a) const
		{return m_domain.Mod(m_domain.Square(a), m_modulus);}

	typename QuotientRing<T>::Element MultiplicativeInverse(const typename T::Element &a) const;

protected:
	const EuclideanDomain &m_domain;
	typename T::Element m_modulus;
};

///////////////////////////////////////////////////////////////////////////////

///////////////////////////////////////////////////////////////////////////////
// BEGIN TEMPLATE DEFINITIONS

#include <vector>
//USING_NAMESPACE(std)

template <class T> T AbstractGroup<T>::Double(const Element &a) const
{
	return Add(a, a);
}

template <class T> T AbstractGroup<T>::Subtract(const Element &a, const Element &b) const
{
	return Add(a, Inverse(b));
}

template <class T> T& AbstractGroup<T>::Accumulate(Element &a, const Element &b) const
{
	return a = Add(a, b);
}

template <class T> T& AbstractGroup<T>::Reduce(Element &a, const Element &b) const
{
	return a = Subtract(a, b);
}

template <class T> T AbstractRing<T>::Square(const Element &a) const
{
	return Multiply(a, a);
}

template <class T> T AbstractRing<T>::Divide(const Element &a, const Element &b) const
{
	return Multiply(a, MultiplicativeInverse(b));
}

template <class T> T AbstractEuclideanDomain<T>::Mod(const Element &a, const Element &b) const
{
	Element r, q;
	DivisionAlgorithm(r, q, a, b);
	return r;
}

template <class T> T AbstractEuclideanDomain<T>::Gcd(const Element &a, const Element &b) const
{
	Element g[3]={b, a};
	unsigned int i0=0, i1=1, i2=2;

	while (!Equal(g[i1], this->Zero()))
	{
		g[i2] = Mod(g[i0], g[i1]);
		unsigned int t = i0; i0 = i1; i1 = i2; i2 = t;
	}

	return g[i0];
}

template <class T> typename QuotientRing<T>::Element QuotientRing<T>::MultiplicativeInverse(const typename T::Element &a) const
{
	typename T::Element g[3]={m_modulus, a};
	typename T::Element v[3]={m_domain.Zero(), m_domain.One()};
	typename T::Element y;
	unsigned int i0=0, i1=1, i2=2;

	while (!Equal(g[i1], Zero()))
	{
		// y = g[i0] / g[i1];
		// g[i2] = g[i0] % g[i1];
		m_domain.DivisionAlgorithm(g[i2], y, g[i0], g[i1]);
		// v[i2] = v[i0] - (v[i1] * y);
		v[i2] = m_domain.Subtract(v[i0], m_domain.Multiply(v[i1], y));
		unsigned int t = i0; i0 = i1; i1 = i2; i2 = t;
	}

	return m_domain.IsUnit(g[i0]) ? m_domain.Divide(v[i0], g[i0]) : m_domain.Zero();
}

template <class T> T AbstractGroup<T>::IntMultiply(const Element &base, const Integer &exponent) const
{
	unsigned int expLen = exponent.BitCount();
	if (expLen==0)
		return Zero();

	unsigned powerTableSize = (expLen <= 17 ? 1 : (expLen <= 24 ? 2 : (expLen <= 70 ? 4 : (expLen <= 197 ? 8 : (expLen <= 539 ? 16 : (expLen <= 1434 ? 32 : 64))))));
	std::vector<Element> powerTable(powerTableSize);

	powerTable[0] = base;
	if (powerTableSize > 1)
	{
		Element temp = Double(base);
		for (unsigned i=1; i<powerTableSize; i++)
			powerTable[i] = Add(temp, powerTable[i-1]);
	}

	Element result;
	unsigned power = 0, prevPosition = expLen-1;
	bool firstTime = true;

	for (int i = expLen-1; i>=0; i--)
	{
		power = 2*power + exponent.GetBit(i);

		if (i==0 || power >= powerTableSize)
		{
			unsigned squaresBefore = prevPosition-i;
			unsigned squaresAfter = 0;
			prevPosition = i;
			while (power && power%2 == 0)
			{
				power /= 2;
				squaresBefore--;
				squaresAfter++;
			}
			if (firstTime)
			{
				result = powerTable[(power-1)/2];
				firstTime = false;
			}
			else
			{
				while (squaresBefore--)
					result = Double(result);
				if (power)
					result = Add(powerTable[(power-1)/2], result);
			}
			while (squaresAfter--)
				result = Double(result);
			power = 0;
		}
	}
	return result;
}

template <class T> T AbstractGroup<T>::CascadeIntMultiply(const Element &x, const Integer &e1, const Element &y, const Integer &e2) const
{
	const unsigned expLen = STDMAX(e1.BitCount(), e2.BitCount());
	if (expLen==0)
		return Zero();

	const unsigned w = (expLen <= 46 ? 1 : (expLen <= 260 ? 2 : 3));
	const unsigned tableSize = 1<<w;
	std::vector<Element> powerTable(tableSize << w);

	powerTable[1] = x;
	powerTable[tableSize] = y;
	if (w==1)
		powerTable[3] = Add(x,y);
	else
	{
		powerTable[2] = Double(x);
		powerTable[2*tableSize] = Double(y);

		unsigned i, j;

		for (i=3; i<tableSize; i+=2)
			powerTable[i] = Add(powerTable[i-2], powerTable[2]);
		for (i=1; i<tableSize; i+=2)
			for (j=i+tableSize; j<(tableSize<<w); j+=tableSize)
				powerTable[j] = Add(powerTable[j-tableSize], y);

		for (i=3*tableSize; i<(tableSize<<w); i+=2*tableSize)
			powerTable[i] = Add(powerTable[i-2*tableSize], powerTable[2*tableSize]);
		for (i=tableSize; i<(tableSize<<w); i+=2*tableSize)
			for (j=i+2; j<i+tableSize; j+=2)
				powerTable[j] = Add(powerTable[j-1], x);
	}

	Element result;
	unsigned power1 = 0, power2 = 0, prevPosition = expLen-1;
	bool firstTime = true;

	for (int i = expLen-1; i>=0; i--)
	{
		power1 = 2*power1 + e1.GetBit(i);
		power2 = 2*power2 + e2.GetBit(i);

		if (i==0 || 2*power1 >= tableSize || 2*power2 >= tableSize)
		{
			unsigned squaresBefore = prevPosition-i;
			unsigned squaresAfter = 0;
			prevPosition = i;
			while ((power1 || power2) && power1%2 == 0 && power2%2==0)
			{
				power1 /= 2;
				power2 /= 2;
				squaresBefore--;
				squaresAfter++;
			}
			if (firstTime)
			{
				result = powerTable[(power2<<w) + power1];
				firstTime = false;
			}
			else
			{
				while (squaresBefore--)
					result = Double(result);
				if (power1 || power2)
					result = Add(powerTable[(power2<<w) + power1], result);
			}
			while (squaresAfter--)
				result = Double(result);
			power1 = power2 = 0;
		}
	}
	return result;
}

template <class Element, class Iterator> Element GeneralCascadeMultiplication(const AbstractGroup<Element> &group, Iterator begin, Iterator end)
{
	if (end-begin == 1)
		return group.IntMultiply((*begin).second, (*begin).first);
	else if (end-begin == 2)
		return group.CascadeIntMultiply((*begin).second, (*begin).first, (*(begin+1)).second, (*(begin+1)).first);
	else
	{
		Integer q, r;
		Iterator last = end;
		--last;

		make_heap(begin, end);
		pop_heap(begin, end);

		while (!!(*begin).first)
		{
			// (*last).first is largest exponent, (*begin).first is next largest
			Integer::Divide(r, q, (*last).first, (*begin).first);

			if (q == Integer::One())
				group.Accumulate((*begin).second, (*last).second);	// avoid overhead of GeneralizedMultiplication()
			else
				group.Accumulate((*begin).second, group.IntMultiply((*last).second, q));

			(*last).first = r;

			push_heap(begin, end);
			pop_heap(begin, end);
		}

		return group.IntMultiply((*last).second, (*last).first);
	}
}

template <class T> T AbstractRing<T>::Exponentiate(const Element &base, const Integer &exponent) const
{
	return MultiplicativeGroup<AbstractRing<T> >(*this).IntMultiply(base, exponent);
}

template <class T> T AbstractRing<T>::CascadeExponentiate(const Element &x, const Integer &e1, const Element &y, const Integer &e2) const
{
	return MultiplicativeGroup<AbstractRing<T> >(*this).CascadeIntMultiply(x, e1, y, e2);
}

#if defined(BREAK_GCC34)
template <class Element, class Iterator> Element GeneralCascadeExponentiation(const AbstractRing<Element> &ring, Iterator begin, Iterator end)
{
	MultiplicativeGroup<AbstractRing<Element> > mg(field);
	return GeneralCascadeMultiplication<Element>(mg, begin, end);
}
#endif /* BREAK_GCC34 */

#endif