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());
  }

}