计算圆周率

[code]import java.math.BigDecimal;
import java.util.Date;

/**
 * <p>
 * Title:π 圆周率的计算
 * </p>
 * <p>
 * Description:使用java BigDecimal完成圆周率(Chudnovsky公式)的计算。可以指定计算精度和计算参数。
 * </p>
 */

public class TestPi {

    private BigDecimal result;

    public void run(int n, int scale) {
        if (System.getProperty("debug") != null) {
            System.out.println("n=" + n);
        }

        BigDecimal upper = new BigDecimal(426880.0000 * Math.sqrt(10005.0000));
        upper = upper.setScale(scale, BigDecimal.ROUND_HALF_EVEN);

        if (System.getProperty("debug") != null) {
            System.out.println("upper=" + upper);
        }

        BigDecimal downer = BigDecimal.valueOf(0);

        for (int i = 0; i <= n; i++) {
            BigDecimal d0 = factorial(6 * i).multiply(
                    new BigDecimal(545140134 * i + 13591409));
            BigDecimal d1 = factorial(i);
            BigDecimal d2 = pow(d1, 3);
            BigDecimal d3 = factorial(3 * i);
            BigDecimal d4 = pow(-640320, 3 * i);
            BigDecimal d5 = d2.multiply(d3);
            BigDecimal d6 = d4.multiply(d5);
            BigDecimal d = d0.divide(d6, BigDecimal.ROUND_HALF_EVEN);

            downer = downer.add(d);

        }

        if (System.getProperty("debug") != null) {
            System.out.println("downer=" + downer);
        }

        if (System.getProperty("debug") != null) {
            System.out.println("upper.scale = " + upper.scale());
            System.out.println("downer.scale = " + downer.scale());
        }

        result = upper.divide(downer, BigDecimal.ROUND_HALF_EVEN);

        if (System.getProperty("debug") != null) {
            System.out.println("result.scale = " + result.scale());
        }

    }

    public BigDecimal getResult() {

        return result;
    }

    public static BigDecimal pow(double val, int power) {
        return pow(new BigDecimal(val), power);
    }

    public static BigDecimal pow(BigDecimal val, int power) {
        BigDecimal value = BigDecimal.valueOf(1);
        for (int i = 1; i <= power; i++) {
            value = value.multiply(val);
        }
        return value;
    }

    public static BigDecimal factorial(int n) {
        BigDecimal value = BigDecimal.valueOf(1);
        for (int i = 1; i <= n; i++) {
            value = value.multiply(BigDecimal.valueOf(i));
        }
        return value;
    }

    public static void main(String[] args) {
        // if(args.length < 2){
        // System.out.println("usage: " + "java nz-baby.Pi " +
        // " 参数(0-无穷大) 精度(1-4294967296)");
        // System.out.println("usage: " + "java nz-baby.Pi " +
        // " n(0- ) scale(1-4294967296)");
        // System.exit(-1);
        // }

        int n = Integer.parseInt("2000");
        int scale = Integer.parseInt("4000");

        System.out.println("palgorithm n=" + n + " scale=" + scale);
        long l = System.currentTimeMillis();
        System.out.println("start:" + new Date(System.currentTimeMillis()));
        TestPi p = new TestPi();
        p.run(n, scale);
        System.out.println("end:" + (System.currentTimeMillis() - l));
        System.out.println("result=" + p.getResult());
    }

}