PiMachinBig2.scala

import java.math.{BigDecimal => BD, MathContext}
import BD.{ZERO, ONE}

/**
 * This program will calculate Pi with John Machin[1]'s formula[2].
 * This is just a translation from Mr. Kishida's Java implementation[3] to
 * Scala one.
 *
 * [1] http://en.wikipedia.org/wiki/John_Machin
 * [2] http://upload.wikimedia.org/math/f/1/5/f15dc3d39c473c4bd718e3a98145da0d.png
 * [3] http://d.hatena.ne.jp/nowokay/20081116#1226837247
 */

object PiMachinBig2{
  def main(arg:Array[String]){
    val mc=new MathContext(100)
    implicit def toBD(i:Int) = new BD(i, mc)
    implicit def foo(i:BD) = new {
      def /(j:BD) = i.divide(j, mc)
      def +(j:BD) = i.add(j)
      def *(j:BD) = i.multiply(j)
      def -(j:BD) = i.subtract(j, mc)
      def unary_- = i.negate
    }

    var sig = ONE
    var a, b = ZERO
    val d5 = 5
    val d239 = 239
    var s1 = ONE / d5
    var s2 = ONE / d239
    val d5_2:BD = d5*d5
    val d239_2:BD = d239*d239
    println("start")
    val start=System.nanoTime
    for(i<-(1 until 140 by 2)){
      a = a + ((s1 / i) * sig)
      b = b + ((s2 / i) * sig)
      s1 = s1 / d5_2
      s2 = s2 / d239_2
      sig = - sig
    }
    println((System.nanoTime-start) / 1000 / 1000  / 1000.)
    a = a * 16
    b = b * 4
    println(a - b)
  }
}