vqc.java v0.1

import java.util.Scanner;
import java.math.BigInteger;

public class vqc{

    private static final BigInteger minusOne = BigInteger.valueOf(-1);
    private static final BigInteger zero = BigInteger.valueOf(0);
    private static final BigInteger one = BigInteger.valueOf(1);
    private static final BigInteger two = BigInteger.valueOf(2);
    private static final BigInteger four = BigInteger.valueOf(4);

    public static void main(String[] args){
        Scanner scan = new Scanner(System.in);
        System.out.println("c=");
        BigInteger c = zero;
        try{
            c = new BigInteger(scan.nextLine());
        } catch(Exception e){
            System.err.println("c is supposed to be a number");
            return;
        }
        while((c.mod(four)).equals(two)){
            c = c.divide(two);
        }
        BigInteger d = sqrt(c);
        BigInteger e = c.subtract(d.multiply(d));
        BigInteger n = factor(d, e);
    }

    public static BigInteger factor(BigInteger d, BigInteger e){
        BigInteger c = (d.multiply(d)).add(e);
        BigInteger cBigNx = c.subtract(d);
        BigInteger cBigNt = zero;
        if((e.mod(two)).equals(zero)){
            cBigNt = (cBigNx.add(two)).divide(two);
        } else {
            cBigNt = (cBigNx.add(one)).divide(two);
        }

        Element aLow = e1Element(e, zero); //t=0
        Element aHigh = e1Element(e, cBigNt); //a[t]=c*BigN
/*
        while(!((aLow.a()).equals(aHigh.a()))){
            if(isOddType1(c)){
                //something
            } else if(isOddType2(c)){
                //something
            } else if(isOddType3(c)){
                //something
            } else if(isOddType4(c)){
                //something
            }
        }
*/
        return zero;
    }

    public static BigInteger sqrt(BigInteger x) {
        if(x.compareTo(zero) == -1){
            x = x.multiply(minusOne);
        }
        if(x.equals(zero)){
            return zero;
        }
        BigInteger div = zero.setBit(x.bitLength()/2);
        BigInteger div2 = div;
        BigInteger returnvalue = zero;
        for(;;) {
            BigInteger y = div.add(x.divide(div)).shiftRight(1);
            if (y.equals(div) || y.equals(div2)){
                returnvalue = y;
                break;
            }
            div2 = div;
            div = y;
        }

        BigInteger testsquare = returnvalue.multiply(returnvalue);
        BigInteger testp1square = (returnvalue.add(one)).multiply(returnvalue.add(one));
        if((testsquare.equals(x)) || (((testsquare.compareTo(x)) == -1) && ((testp1square.compareTo(x)) == 1))){
            return returnvalue;
        } else {
            return returnvalue.subtract(one);
        }
    }

    public static Element e1Element(BigInteger e, BigInteger t){
        BigInteger x = zero;
        if((e.mod(two)).equals(zero)){
            x = (t.subtract(one)).multiply(two);
        } else {
            x = (t.multiply(two)).subtract(one);
        }

        BigInteger xx = x.multiply(x);
        BigInteger xxpe = xx.add(e);
        BigInteger a = ((x.multiply(x)).add(e)).divide(two);
        BigInteger b = a.add(x.multiply(two)).add(two);

        if(e.compareTo(zero) == -1){
            return new Element(a, b, e); //(f,1)
        } else {
            return new Element(a, b); //(e,1)
        }
    }
}