doublehelper.java

一个非常有用的操作MCRSOFT EXCEL文件的工具。可以用JAVA方便的新建

/*********************************************************************
*
*      Copyright (C) 2001 Andrew Khan
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
***************************************************************************/

package jxl.biff;

/**
 * Class to help handle doubles
 */
public class DoubleHelper
{
  /**
   * Private constructor to prevent instantiation
   */
  private DoubleHelper()
  {
  }

  /**
   * Gets the IEEE value from the byte array passed in
   *
   * @param pos the position in the data block which contains the double value
   * @param data the data block containing the raw bytes
   * @return the double value converted from the raw data
   */
  public static double getIEEEDouble(byte[] data, int pos)
  {
    int num1 = IntegerHelper.getInt(data[pos], data[pos + 1],
                                    data[pos + 2], data[pos + 3]);
    int num2 = IntegerHelper.getInt(data[pos + 4], data[pos + 5],
                                    data[pos + 6], data[pos + 7]);

    // Long.parseLong doesn't like the sign bit, so have to extract this
    // information and put it in at the end.  (Acknowledgment:  thanks
    // to Ruben for pointing this out)
    boolean negative = ((num2 & 0x80000000) != 0);

    // Thanks to Lyle for the following improved IEEE double processing
    long val = ((num2 & 0x7fffffff) * 0x100000000L) +
                  (num1 < 0 ? 0x100000000L + num1 : num1);
    double value = Double.longBitsToDouble(val);

    if (negative)
    {
      value = -value;
    }
    return value;
  }

  /**
   * Puts the IEEE representation of the double provided into the array
   * at the designated position
   *
   * @param target the data block into which the binary representation is to
   *     be placed
   * @param pos the position in target in which to place the bytes
   * @param d the double value to convert to raw bytes
   */
  public static void getIEEEBytes(double d, byte[] target, int pos)
  {
    long val = Double.doubleToLongBits(d);
    target[pos]   = (byte) (val & 0xff);
    target[pos + 1] = (byte) ((val & 0xff00) >> 8);
    target[pos + 2] = (byte) ((val & 0xff0000) >> 16);
    target[pos + 3] = (byte) ((val & 0xff000000) >> 24);
    target[pos + 4] = (byte) ((val & 0xff00000000L) >> 32);
    target[pos + 5] = (byte) ((val & 0xff0000000000L) >> 40);
    target[pos + 6] = (byte) ((val & 0xff000000000000L) >> 48);
    target[pos + 7] = (byte) ((val & 0xff00000000000000L) >> 56) ;
  }
}