code: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements. See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership. The ASF licenses this file
   * to you under the Apache License, Version 2.0 (the  "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  /*
   * $Id$
   */
  package org.apache.xpath.functions;
  
  import org.apache.xalan.res.XSLMessages;
  import org.apache.xml.utils.XMLString;
  import org.apache.xpath.XPathContext;
  import org.apache.xpath.objects.XObject;
  import org.apache.xpath.objects.XString;
  import org.apache.xpath.res.XPATHErrorResources;
  
  /**
   * Execute the Substring() function.
   * @xsl.usage advanced
   */
  public class FuncSubstring extends Function3Args
  {
      static final long serialVersionUID = -5996676095024715502L;
  
    /**
     * Execute the function.  The function must return
     * a valid object.
     * @param xctxt The current execution context.
     * @return A valid XObject.
     *
     * @throws javax.xml.transform.TransformerException
     */
    public XObject execute(XPathContext xctxt) throws javax.xml.transform.TransformerException
    {
  
      XMLString s1 = m_arg0.execute(xctxt).xstr();
      double start = m_arg1.execute(xctxt).num();
      int lenOfS1 = s1.length();
      XMLString substr;
  
      if (lenOfS1 <= 0)
        return XString.EMPTYSTRING;
      else
      {
        int startIndex;
  
        if (Double.isNaN(start))
        {
  
          // Double.MIN_VALUE doesn't work with math below 
          // so just use a big number and hope I never get caught.
          start = -1000000;
          startIndex = 0;
        }
        else
        {
          start = Math.round(start);
          startIndex = (start > 0) ? (int) start - 1 : 0;
        }
  
        if (null != m_arg2)
        {
          double len = m_arg2.num(xctxt);
          int end = (int) (Math.round(len) + start) - 1;
  
          // Normalize end index.
          if (end < 0)
            end = 0;
          else if (end > lenOfS1)
            end = lenOfS1;
  
          if (startIndex > lenOfS1)
            startIndex = lenOfS1;
  
          substr = s1.substring(startIndex, end);
        }
        else
        {
          if (startIndex > lenOfS1)
            startIndex = lenOfS1;
          substr = s1.substring(startIndex);
        }
      }
  
      return (XString)substr; // cast semi-safe
    }
  
    /**
     * Check that the number of arguments passed to this function is correct. 
     *
     *
     * @param argNum The number of arguments that is being passed to the function.
     *
     * @throws WrongNumberArgsException
     */
    public void checkNumberArgs(int argNum) throws WrongNumberArgsException
    {
      if (argNum < 2)
        reportWrongNumberArgs();
    }
  
    /**
     * Constructs and throws a WrongNumberArgException with the appropriate
     * message for this function object.
     *
     * @throws WrongNumberArgsException
     */
    protected void reportWrongNumberArgs() throws WrongNumberArgsException {
        throw new WrongNumberArgsException(XSLMessages.createXPATHMessage(XPATHErrorResources.ER_TWO_OR_THREE, null)); //"2 or 3");
    }
  }
  