package chu_nz_baby;

import java.util.*;

import java.math.*;

/**

* <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>

* <p>Copyright: Copyright (c) 2004</p>

* <a href="http://www.jason314.com/palgorithm.htm">圆周率的计算方法#Chudnovsky公式</a>

* <a href="http://www.oursci.org/magazine/200301/030126.htm">圆周率π的计算历程</a>

* @author chu_nz_baby@hotmail.com

* @version 1.0

*/

public class Pi {

 private BigDecimal result;

 public Pi() {

 }

 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(args[0]);

  int scale = Integer.parseInt(args[1]);

  System.out.println("palgorithm n=" + n + " scale=" + scale);

  System.out.println("start:" + new Date(System.currentTimeMillis()));

  Pi p = new Pi();

  p.run(n, scale);

  System.out.println("end:" + new Date(System.currentTimeMillis()));

  System.out.println("result=" + p.getResult());

 }

}