Compute PI

JoinDemo

package couchbase.test;

import java.math.BigDecimal;

public class JoinDemo {

	private final static BigDecimal FOUR = BigDecimal.valueOf(4);
	private final static int roundingMode = BigDecimal.ROUND_HALF_EVEN;

	private static BigDecimal result;
	
	public static void main(String[] args) {
		Runnable r = () -> {
			result = JoinDemo(50_000);
		};
		Thread t = new Thread(r);
		t.start();
		try{
			System.out.println("Joining..");
			t.join();
		}catch (Exception e) {
			System.out.println(e);
		}
		
		System.out.println(result);
	}
	
	
	public static BigDecimal computePi(int digits){
		int scale = digits + 5;
		BigDecimal arctan1_5 = arctan(5, scale);
		BigDecimal arctan239 = arctan(239, scale);
		BigDecimal pi = arctan1_5.multiply(FOUR)
						.subtract(arctan239).multiply(FOUR);
		
		return pi.setScale(digits, BigDecimal.ROUND_HALF_UP);
	}


	private static BigDecimal arctan(int invertX, int scale) {
		BigDecimal result, number, term;
		BigDecimal invX = BigDecimal.valueOf(invertX);
		BigDecimal invX2 = BigDecimal.valueOf(invertX * invertX);
		number = BigDecimal.ONE.divide(invX, scale, roundingMode);
		result = number;
		int i = 1;
		do{
			number = number.divide(invX2, scale, roundingMode);
			int denom = 2 * i + 1;
			term = number.divide(BigDecimal.valueOf(denom), scale, roundingMode);
			if((i % 2) != 0)
					result = result.subtract(term);
			else
					result =result.add(term);
			i++;
		}	
		while(term.compareTo(BigDecimal.ZERO) != 0);
		return result;
	}
}