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  1. /*
  2.  * Copyright (c) 2008, Manuel Mausz <manuel at mausz.at>
  3.  * All rights reserved.
  4.  *
  5.  * Redistribution and use in source and binary forms, with or without
  6.  * modification, are permitted provided that the following conditions are met:
  7.  *     * Redistributions of source code must retain the above copyright
  8.  *       notice, this list of conditions and the following disclaimer.
  9.  *     * Redistributions in binary form must reproduce the above copyright
  10.  *       notice, this list of conditions and the following disclaimer in the
  11.  *       documentation and/or other materials provided with the distribution.
  12.  *     * Neither the name of the copyright holders nor the
  13.  *       names of its contributors may be used to endorse or promote products
  14.  *       derived from this software without specific prior written permission.
  15.  *
  16.  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  17.  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  18.  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  19.  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  20.  * HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  21.  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
  22.  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
  23.  * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  24.  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
  25.  * TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
  26.  * USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
  27.  * DAMAGE.
  28.  */
  29.  
  30. import java.util.Stack;
  31.  
  32. /**
  33.  * Implements mathematical invers (1/x)
  34.  *
  35.  * @version 1.0
  36.  * @author  Manuel Mausz (manuel at mausz.at)
  37.  * @author  http://manuel.mausz.at/
  38.  */
  39. class InvOperation implements UPNOperation
  40. {
  41.   /**
  42.    * constructor
  43.    */
  44.   public InvOperation()
  45.   {
  46.   }
  47.  
  48.   /**
  49.    * returns operations symbol
  50.    *
  51.    * @return operation symbol
  52.    */
  53.   public String getOperationSymbol()
  54.   {
  55.     return "inv";
  56.   }
  57.  
  58.   /**
  59.    * performs the actual execution
  60.    *
  61.    * @param op stack to retrieve the values from
  62.    */
  63.   public void execute (Stack<Double> op)
  64.     throws InvalidParameterException
  65.   {
  66.     double v1, res;
  67.  
  68.     if (op.empty())
  69.       throw new InvalidParameterException("Insuifficent operands on stack");
  70.     v1 = op.pop();
  71.     if (Math.abs(v1) < EPSILON)
  72.       v1 = 0;
  73.  
  74.     res = 1 / v1;
  75.     if (Math.abs(res) < EPSILON)
  76.       res = 0;
  77.     op.push(res);
  78.   }
  79. }
  80.