Java PI Generation – Gregory-Leibniz

Java program to generate PI digits using Gregory-Leibniz series using double and BigDecimal.

After 500.000 iterations as expected it generates only 5 correct decimal digits.

3.141590653589692028191393546876497566699981689453125
3.1415906535897932404626433832695028841972913993751030509749446933498164008806789990267567873033589959

import java.math.BigDecimal;
import java.math.RoundingMode;

// ? 2019 TheFlyingKeyboard and released under MIT License
// theflyingkeyboard.net

public class Main {

    private static final int scale = 100;

    public static void main(String[] args) {
        long iterations = 500000;

        System.out.println(new BigDecimal(gregoryLeibnitz(iterations)));
        System.out.println(gregoryLeibnitzBigDecimal(iterations));
    }

    private static double gregoryLeibnitz(long iterations) {
        double pi = 0;
        double divisor = 1;

        for (long i = 0; i < iterations; ++i) {
            pi += i % 2 == 0 ? 4.0d / divisor : -4.0d / divisor;
            divisor += 2;
        }

        return pi;
    }

    private static BigDecimal gregoryLeibnitzBigDecimal(long iterations) {
        BigDecimal pi = new BigDecimal(0);
        BigDecimal divisor = new BigDecimal(1);
        BigDecimal dividend = new BigDecimal(4);
        BigDecimal divisorStep = new BigDecimal(2);

        for (long i = 0; i < iterations; ++i) {
            pi = pi.add(i % 2 == 0 ?
                    dividend.divide(divisor, scale, RoundingMode.CEILING) :
                    dividend.divide(divisor.negate(), scale, RoundingMode.CEILING));
            divisor = divisor.add(divisorStep);
        }

        return pi;
    }

}