/*
Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements.  See the NOTICE file
distributed with this work for additional information
regarding copyright ownership.  The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License.  You may obtain a copy of the License at

  http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, either express or implied.  See the License for the
specific language governing permissions and limitations
under the License.
*/

/* Finite Field arithmetic  Fp^16 functions */

/* FP16 elements are of the form a+ib, where i is sqrt(sqrt(sqrt(-1+sqrt(-1))))  */

package org.apache.milagro.amcl.XXX;

public final class FP16 {
	private final FP8 a;
	private final FP8 b;
/* reduce all components of this mod Modulus */
	public void reduce()
	{
		a.reduce();
		b.reduce();
	}
/* normalise all components of this mod Modulus */
	public void norm()
	{
		a.norm();
		b.norm();
	}
/* test this==0 ? */
	public boolean iszilch() {
		return (a.iszilch() && b.iszilch());
	}

	public void cmove(FP16 g,int d)
	{
		a.cmove(g.a,d);
		b.cmove(g.b,d);
	}

/* test this==1 ? */
	public boolean isunity() {
		FP8 one=new FP8(1);
		return (a.equals(one) && b.iszilch());
	}

/* test is w real? That is in a+ib test b is zero */
	public boolean isreal()
	{
		return b.iszilch();
	}
/* extract real part a */
	public FP8 real()
	{
		return a;
	}

	public FP8 geta()
	{
		return a;
	}
/* extract imaginary part b */
	public FP8 getb()
	{
		return b;
	}
/* test this=x? */
	public boolean equals(FP16 x)
	{
		return (a.equals(x.a) && b.equals(x.b));
	}
/* constructors */
	public FP16(int c)
	{
		a=new FP8(c);
		b=new FP8(0);
	}

	public FP16(FP16 x)
	{
		a=new FP8(x.a);
		b=new FP8(x.b);
	}

	public FP16(FP8 c,FP8 d)
	{
		a=new FP8(c);
		b=new FP8(d);
	}

	public FP16(FP8 c)
	{
		a=new FP8(c);
		b=new FP8(0);
	}
/* copy this=x */
	public void copy(FP16 x)
	{
		a.copy(x.a);
		b.copy(x.b);
	}
/* set this=0 */
	public void zero()
	{
		a.zero();
		b.zero();
	}

/* set this=1 */
	public void one()
	{
		a.one();
		b.zero();
	}
/* set this=-this */
	public void neg()
	{
		norm();
		FP8 m=new FP8(a);
		FP8 t=new FP8(0);
		m.add(b);
		m.neg();
		t.copy(m); t.add(b);
		b.copy(m);
		b.add(a);
		a.copy(t);
		norm();
	}

/* this=conjugate(this) */
	public void conj()
	{
		b.neg(); norm();
	}
/* this=-conjugate(this) */
	public void nconj()
	{
		a.neg(); norm();
	}
/* this+=x */
	public void add(FP16 x)
	{
		a.add(x.a);
		b.add(x.b);
	}
/* this-=x */
	public void sub(FP16 x)
	{
		FP16 m=new FP16(x);
		m.neg();
		add(m);
	}

/* this=x-this */
	public void rsub(FP16 x)
	{
		neg();
		add(x);
	}

/* this*=s where s is FP8 */
	public void pmul(FP8 s)
	{
		a.mul(s);
		b.mul(s);
	}
/* this*=s where s is FP2 */
	public void qmul(FP2 s)
	{
		a.qmul(s);
		b.qmul(s);
	}

/* this*=c where c is int */
	public void imul(int c)
	{
		a.imul(c);
		b.imul(c);
	}

/* this*=this */	
	public void sqr()
	{
		FP8 t1=new FP8(a);
		FP8 t2=new FP8(b);
		FP8 t3=new FP8(a);

		t3.mul(b);
		t1.add(b);
		t2.times_i();

		t2.add(a);

		t1.norm();
		t2.norm();

		a.copy(t1);

		a.mul(t2);

		t2.copy(t3);
		t2.times_i();
		t2.add(t3);
		t2.norm();
		t2.neg();
		a.add(t2);

		b.copy(t3);
		b.add(t3);

		norm();
	}

/* this*=y */
	public void mul(FP16 y)
	{
		FP8 t1=new FP8(a);
		FP8 t2=new FP8(b);
		FP8 t3=new FP8(0);
		FP8 t4=new FP8(b);

		t1.mul(y.a);
		t2.mul(y.b);
		t3.copy(y.b);
		t3.add(y.a);
		t4.add(a);

		t3.norm();
		t4.norm();

		t4.mul(t3);

		t3.copy(t1);
		t3.neg();
		t4.add(t3);
		t4.norm();

		t3.copy(t2);
		t3.neg();
		b.copy(t4);
		b.add(t3);

		t2.times_i();
		a.copy(t2);
		a.add(t1);

		norm();
	}

/* convert this to hex string */
	public String toString() 
	{
		return ("["+a.toString()+","+b.toString()+"]");
	}

/* this=1/this */
	public void inverse()
	{
		FP8 t1=new FP8(a);
		FP8 t2=new FP8(b);

		t1.sqr();
		t2.sqr();
		t2.times_i();
		t2.norm();
		t1.sub(t2); t1.norm();
		t1.inverse();
		a.mul(t1);
		t1.neg();
		t1.norm();
		b.mul(t1);
	}

/* this*=i where i = sqrt(-1+sqrt(-1)) */
	public void times_i()
	{
		FP8 s=new FP8(b);
		FP8 t=new FP8(a);
		s.times_i();
		b.copy(t);
		a.copy(s);
		norm();
	}

	public void times_i2()
	{
		a.times_i();
		b.times_i();
	}

	public void times_i4()
	{
		a.times_i2();
		b.times_i2();
	}

/* this=this^p using Frobenius */
	public void frob(FP2 f)
	{
		FP2 ff=new FP2(f); ff.sqr(); ff.norm();

		a.frob(ff);
		b.frob(ff);
		b.qmul(f);
		b.times_i();
	}

/* this=this^e */
	public FP16 pow(BIG e)
	{
		FP16 w=new FP16(this);
		w.norm();
		BIG z=new BIG(e);
		FP16 r=new FP16(1);
		z.norm();
		while (true)
		{
			int bt=z.parity();
			z.fshr(1);
			if (bt==1) r.mul(w);
			if (z.iszilch()) break;
			w.sqr();
		}
		r.reduce();
		return r;
	}

/* XTR xtr_a function */
	public void xtr_A(FP16 w,FP16 y,FP16 z) 
	{
		FP16 r=new FP16(w);
		FP16 t=new FP16(w);
	
		r.sub(y);
		r.norm();
		r.pmul(a);
		t.add(y);
		t.norm();
		t.pmul(b);
		t.times_i();

		copy(r);
		add(t);
		add(z);

		norm();
	}

/* XTR xtr_d function */
	public void xtr_D() {
		FP16 w=new FP16(this);
		sqr(); w.conj();
		w.add(w);
		w.norm();
		sub(w);
		reduce();
	}

/* r=x^n using XTR method on traces of FP12s */
	public FP16 xtr_pow(BIG n) {
		FP16 sf=new FP16(this);
		sf.norm();
		FP16 a=new FP16(3);
		FP16 b=new FP16(sf);
		FP16 c=new FP16(b);
		c.xtr_D();
		FP16 t=new FP16(0);
		FP16 r=new FP16(0);

		
		int par=n.parity();
		BIG v=new BIG(n); v.norm(); v.fshr(1);
		if (par==0) {v.dec(1); v.norm();}

		int nb=v.nbits();
		for (int i=nb-1;i>=0;i--)
		{
			if (v.bit(i)!=1)
			{
				t.copy(b);
				sf.conj();
				c.conj();
				b.xtr_A(a,sf,c);
				sf.conj();
				c.copy(t);
				c.xtr_D();
				a.xtr_D();
			}
			else
			{
				t.copy(a); t.conj();
				a.copy(b);
				a.xtr_D();
				b.xtr_A(c,sf,t);
				c.xtr_D();
			}
		}
		if (par==0) r.copy(c);
		else r.copy(b);
		r.reduce();
		return r;
	}

/* r=ck^a.cl^n using XTR double exponentiation method on traces of FP12s. See Stam thesis. */
	public FP16 xtr_pow2(FP16 ck,FP16 ckml,FP16 ckm2l,BIG a,BIG b)
	{
		BIG e=new BIG(a);
		BIG d=new BIG(b);
		BIG w=new BIG(0);
		d.norm(); d.norm();
		FP16 cu=new FP16(ck);  // can probably be passed in w/o copying
		FP16 cv=new FP16(this);
		FP16 cumv=new FP16(ckml);
		FP16 cum2v=new FP16(ckm2l);
		FP16 r=new FP16(0);
		FP16 t=new FP16(0);

		int f2=0;
		while (d.parity()==0 && e.parity()==0)
		{
			d.fshr(1);
			e.fshr(1);
			f2++;
		}

		while (BIG.comp(d,e)!=0)
		{
			if (BIG.comp(d,e)>0)
			{
				w.copy(e); w.imul(4); w.norm();
				if (BIG.comp(d,w)<=0)
				{
					w.copy(d); d.copy(e);
					e.rsub(w); e.norm();

					t.copy(cv); 
					t.xtr_A(cu,cumv,cum2v);
					cum2v.copy(cumv); 
					cum2v.conj();
					cumv.copy(cv);
					cv.copy(cu);
					cu.copy(t);

				}
				else if (d.parity()==0)
				{
					d.fshr(1);
					r.copy(cum2v); r.conj();
					t.copy(cumv);
					t.xtr_A(cu,cv,r);
					cum2v.copy(cumv);
					cum2v.xtr_D();
					cumv.copy(t);
					cu.xtr_D();
				}
				else if (e.parity()==1)
				{
					d.sub(e); d.norm();
					d.fshr(1);
					t.copy(cv);
					t.xtr_A(cu,cumv,cum2v);
					cu.xtr_D();
					cum2v.copy(cv);
					cum2v.xtr_D();
					cum2v.conj();
					cv.copy(t);
				}
				else
				{
					w.copy(d);
					d.copy(e); d.fshr(1);
					e.copy(w);
					t.copy(cumv);
					t.xtr_D();
					cumv.copy(cum2v); cumv.conj();
					cum2v.copy(t); cum2v.conj();
					t.copy(cv);
					t.xtr_D();
					cv.copy(cu);
					cu.copy(t);
				}
			}
			if (BIG.comp(d,e)<0)
			{
				w.copy(d); w.imul(4); w.norm();
				if (BIG.comp(e,w)<=0)
				{
					e.sub(d); e.norm();
					t.copy(cv);
					t.xtr_A(cu,cumv,cum2v);
					cum2v.copy(cumv);
					cumv.copy(cu);
					cu.copy(t);
				}
				else if (e.parity()==0)
				{
					w.copy(d);
					d.copy(e); d.fshr(1);
					e.copy(w);
					t.copy(cumv);
					t.xtr_D();
					cumv.copy(cum2v); cumv.conj();
					cum2v.copy(t); cum2v.conj();
					t.copy(cv);
					t.xtr_D();
					cv.copy(cu);
					cu.copy(t);
				}
				else if (d.parity()==1)
				{
					w.copy(e);
					e.copy(d);
					w.sub(d); w.norm();
					d.copy(w); d.fshr(1);
					t.copy(cv);
					t.xtr_A(cu,cumv,cum2v);
					cumv.conj();
					cum2v.copy(cu);
					cum2v.xtr_D();
					cum2v.conj();
					cu.copy(cv);
					cu.xtr_D();
					cv.copy(t);
				}
				else
				{
					d.fshr(1);
					r.copy(cum2v); r.conj();
					t.copy(cumv);
					t.xtr_A(cu,cv,r);
					cum2v.copy(cumv);
					cum2v.xtr_D();
					cumv.copy(t);
					cu.xtr_D();
				}
			}
		}
		r.copy(cv);
		r.xtr_A(cu,cumv,cum2v);
		for (int i=0;i<f2;i++)
			r.xtr_D();
		r=r.xtr_pow(d);
		return r;
	}
}