import java.io.IOException;
import java.util.Scanner;
import org.apfloat.ApfloatMath;
import org.apfloat.Apfloat;

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

/**
 *
 * @author Jake Gunter
 */
public class PiSalaminBrent {
    private long precision = 1000;
    private Apfloat[] calculateNums(Apfloat[] lastIter, int iter, int desiredIter) {
        Apfloat[] toReturn = new Apfloat[4];
        toReturn[0] = (lastIter[0].add(lastIter[1])).divide(new Apfloat(2));
        toReturn[1] = ApfloatMath.sqrt(lastIter[0].multiply(lastIter[1]));
        Apfloat x = ApfloatMath.pow((lastIter[0].subtract(toReturn[0])), 2);
        toReturn[2] = lastIter[2].subtract(lastIter[3].multiply(x));
        toReturn[3] = lastIter[3].multiply(new Apfloat(2));
        if (iter == desiredIter) return toReturn;
        return calculateNums(toReturn, ++iter, desiredIter);
    }
    
    private Apfloat calculate2(Apfloat a, int iter, int desiredIter) {
        a = a.subtract(ApfloatMath.tan(a));
        if (iter == desiredIter) return a;
        return calculate2(a, iter+1, desiredIter);
    }
    
    private Apfloat calculateNonic(Apfloat a, int iter, int desiredIter) {
        Apfloat firstTerm = ApfloatMath.tan(a);
        Apfloat secondTerm = (new Apfloat(1, precision).divide(new Apfloat(3, precision))).multiply(ApfloatMath.pow(ApfloatMath.tan(a), 3));
        Apfloat thirdTerm = (new Apfloat(1, precision).divide(new Apfloat(5, precision))).multiply(ApfloatMath.pow(ApfloatMath.tan(a), 5));
        Apfloat fourthTerm = (new Apfloat(1, precision).divide(new Apfloat(7, precision))).multiply(ApfloatMath.pow(ApfloatMath.tan(a), 7));
        return ApfloatMath.sum(a, firstTerm.negate(), secondTerm, thirdTerm.negate(), fourthTerm);
    }
    
    private Apfloat calculateVeryVerySimplest(long precision) {
        return new Apfloat(4, precision).multiply(ApfloatMath.atan(new Apfloat(1, precision)));
    }
    
    private Apfloat calculateSimplest(Apfloat curIter, int iter, int desiredIter) {
        Apfloat toReturn = curIter.add(ApfloatMath.sin(curIter));
        if (iter == desiredIter) return toReturn;
        return calculateSimplest(toReturn, ++iter, desiredIter);
    }
    
    private Apfloat calculateSimpler(long precision) {
        Apfloat a = Apfloat.ONE.divide(ApfloatMath.sqrt(new Apfloat(3, precision)));
        a = ApfloatMath.atan(a);
        return a.multiply(new Apfloat(6, precision));
    }
    
    private Apfloat calculateMachinLikeSimple(long precision) {
        Apfloat oneFifth = Apfloat.ONE.divide(new Apfloat(5, precision));
        Apfloat oneTwoThirtyNinth = Apfloat.ONE.divide(new Apfloat(239, precision));
        Apfloat pi = (new Apfloat(4, precision).multiply(ApfloatMath.atan(oneFifth))).subtract(ApfloatMath.atan(oneTwoThirtyNinth));
        return pi.multiply(new Apfloat(4, precision));
    }
    
    public static void main(String[] args) throws IOException {
        long precision = 10000;
        Scanner in = new Scanner(System.in);
        do {
            System.out.println("\nPI CALCULATOR, V. 3.0");
            System.out.println("----------------------------------");
            System.out.print("How many digits? Type in a number less than 1 to exit. ");
            precision = in.nextLong();
            /*
            Apfloat a = Apfloat.ZERO;
            Apfloat b = Apfloat.ONE.divide(ApfloatMath.sqrt(new Apfloat(2)));
            Apfloat c = new Apfloat(.25);
            Apfloat d = Apfloat.ONE;
            Apfloat[] pi = new PiSalaminBrent().calculateNums(new Apfloat[] {a, b, c, d}, 0, 3);
            Apfloat num = ApfloatMath.pow(pi[0].add(pi[1]), 2);
            Apfloat den = new Apfloat(4).multiply(pi[3]);
            System.out.println((num.divide(den)).toString(true));*/
            if (precision > 0) {
                long start = System.currentTimeMillis();
                Apfloat pi = new PiSalaminBrent().//calculateSimplest(new Apfloat(22, precision).divide(new Apfloat(7, precision)), 0, 2);
                        //calculateSimpler(precision);
                        //calculate2(new Apfloat(22, precision).divide(new Apfloat(7, precision)), 0, 10);
                        //calculateVeryVerySimplest(precision);
                        calculateMachinLikeSimple(precision);
                long total = System.currentTimeMillis() - start;
                System.out.println(pi.toString(true));
                System.out.println("Calculation took " + total + " milliseconds.");
            }
        } while (precision > 0);
        
    }
}