private final int cutoff = 8;

public <T> void perform(Comparable<T>[] a) {
    perform(a,0,a.length - 1);
  }

  private <T> int median3(Comparable<T>[] a,int x,int y,int z) {
    if(lessThan(a[x],a[y])) {
      if(lessThan(a[y],a[z])) {
        return y;
      }
      else if(lessThan(a[x],a[z])) {
        return z;
      }else {
        return x;
      }
    }else {
      if(lessThan(a[z],a[y])){
        return y;
      }else if(lessThan(a[z],a[x])) {
        return z;
      }else {
        return x;
      }
    }
  }

  private <T> void perform(Comparable<T>[] a,int low,int high) {
    int n = high - low + 1;
    //當序列非常小，用插入排序
    if(n <= cutoff) {
      InsertionSort insertionSort = SortFactory.createInsertionSort();
      insertionSort.perform(a,low,high);
      //當序列中小時，使用median3
    }else if(n <= 100) {
      int m = median3(a,low,low + (n >>> 1),high);
      exchange(a,m,low);
      //當序列比較大時，使用ninther
    }else {
      int gap = n >>> 3;
      int m = low + (n >>> 1);
      int m1 = median3(a,low,low + gap,low + (gap << 1));
      int m2 = median3(a,m - gap,m,m + gap);
      int m3 = median3(a,high - (gap << 1),high - gap,high);
      int ninther = median3(a,m1,m2,m3);
      exchange(a,ninther,low);
    }

    if(high <= low)
      return;
    //lessThan
    int lt = low;
    //greaterThan
    int gt = high;
    //中心點
    Comparable<T> pivot = a[low];
    int i = low + 1;

    /*
    * 不變式：
    *  a[low..lt-1] 小于pivot -> 前部(first)
    *  a[lt..i-1] 等于 pivot -> 中部(middle)
    *  a[gt+1..n-1] 大于 pivot -> 后部(final)
    *
    *  a[i..gt] 待考察區(qū)域
    */

    while (i <= gt) {
      if(lessThan(a[i],pivot)) {
        //i-> ,lt ->
        exchange(a,lt++,i++);
      }else if(lessThan(pivot,a[i])) {
        exchange(a,i,gt--);
      }else{
        i++;
      }
    }

    // a[low..lt-1] < v = a[lt..gt] < a[gt+1..high].
    perform(a,low,lt - 1);
    perform(a,gt + 1,high);
  }

 /**
   * 小于等于這個值的時候，交給插入排序
   */
  private final int cutoff = 8;

  /**
   * 對給定的元素序列進行排序
   *
   * @param a 給定元素序列
   */
  @Override
  public <T> void perform(Comparable<T>[] a) {
    Comparable<T>[] b = a.clone();
    perform(b, a, 0, a.length - 1);
  }

  private <T> void perform(Comparable<T>[] src,Comparable<T>[] dest,int low,int high) {
    if(low >= high)
      return;

    //小于等于cutoff的時候,交給插入排序
    if(high - low <= cutoff) {
      SortFactory.createInsertionSort().perform(dest,low,high);
      return;
    }

    int mid = low + ((high - low) >>> 1);
    perform(dest,src,low,mid);
    perform(dest,src,mid + 1,high);

    //考慮局部有序 src[mid] <= src[mid+1]
    if(lessThanOrEqual(src[mid],src[mid+1])) {
      System.arraycopy(src,low,dest,low,high - low + 1);
    }

    //src[low .. mid] + src[mid+1 .. high] -> dest[low .. high]
    merge(src,dest,low,mid,high);
  }

  private <T> void merge(Comparable<T>[] src,Comparable<T>[] dest,int low,int mid,int high) {

    for(int i = low,v = low,w = mid + 1; i <= high; i++) {
      if(w > high || v <= mid && lessThanOrEqual(src[v],src[w])) {
        dest[i] = src[v++];
      }else {
        dest[i] = src[w++];
      }
    }
  }

sort -n bigdata -o bigdata.sorted

 private BitSet bits;

  public void perform(
      String largeFileName,
      int total,
      String destLargeFileName,
      Castor<Integer> castor,
      int readerBufferSize,
      int writerBufferSize,
      boolean asc) throws IOException {

    System.out.println("BitmapSort Started.");
    long start = System.currentTimeMillis();
    bits = new BitSet(total);
    InputPart<Integer> largeIn = PartFactory.createCharBufferedInputPart(largeFileName, readerBufferSize);
    OutputPart<Integer> largeOut = PartFactory.createCharBufferedOutputPart(destLargeFileName, writerBufferSize);
    largeOut.delete();

    Integer data;
    int off = 0;
    try {
      while (true) {
        data = largeIn.read();
        if (data == null)
          break;
        int v = data;
        set(v);
        off++;
      }
      largeIn.close();
      int size = bits.size();
      System.out.println(String.format("lines : %d ,bits : %d", off, size));

      if(asc) {
        for (int i = 0; i < size; i++) {
          if (get(i)) {
            largeOut.write(i);
          }
        }
      }else {
        for (int i = size - 1; i >= 0; i--) {
          if (get(i)) {
            largeOut.write(i);
          }
        }
      }

      largeOut.close();
      long stop = System.currentTimeMillis();
      long elapsed = stop - start;
      System.out.println(String.format("BitmapSort Completed.elapsed : %dms",elapsed));
    }finally {
      largeIn.close();
      largeOut.close();
    }
  }

  private void set(int i) {
    bits.set(i);
  }

  private boolean get(int v) {
    return bits.get(v);
  }