xref: /external/apache-xml/src/main/java/org/apache/xml/utils/FastStringBuffer.java

/*
 * 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: FastStringBuffer.java 469279 2006-10-30 21:18:02Z minchau $
 */
package org.apache.xml.utils;

/**
 * Bare-bones, unsafe, fast string buffer. No thread-safety, no
 * parameter range checking, exposed fields. Note that in typical
 * applications, thread-safety of a StringBuffer is a somewhat
 * dubious concept in any case.
 * <p>
 * Note that Stree and DTM used a single FastStringBuffer as a string pool,
 * by recording start and length indices within this single buffer. This
 * minimizes heap overhead, but of course requires more work when retrieving
 * the data.
 * <p>
 * FastStringBuffer operates as a "chunked buffer". Doing so
 * reduces the need to recopy existing information when an append
 * exceeds the space available; we just allocate another chunk and
 * flow across to it. (The array of chunks may need to grow,
 * admittedly, but that's a much smaller object.) Some excess
 * recopying may arise when we extract Strings which cross chunk
 * boundaries; larger chunks make that less frequent.
 * <p>
 * The size values are parameterized, to allow tuning this code. In
 * theory, Result Tree Fragments might want to be tuned differently
 * from the main document's text.
 * <p>
 * %REVIEW% An experiment in self-tuning is
 * included in the code (using nested FastStringBuffers to achieve
 * variation in chunk sizes), but this implementation has proven to
 * be problematic when data may be being copied from the FSB into itself.
 * We should either re-architect that to make this safe (if possible)
 * or remove that code and clean up for performance/maintainability reasons.
 * <p>
 */
public class FastStringBuffer
{
  // If nonzero, forces the inial chunk size.
  /**/static final int DEBUG_FORCE_INIT_BITS=0;

  	// %BUG% %REVIEW% *****PROBLEM SUSPECTED: If data from an FSB is being copied
  	// back into the same FSB (variable set from previous variable, for example)
  	// and blocksize changes in mid-copy... there's risk of severe malfunction in
  	// the read process, due to how the resizing code re-jiggers storage. Arggh.
  	// If we want to retain the variable-size-block feature, we need to reconsider
  	// that issue. For now, I have forced us into fixed-size mode.
    static final boolean DEBUG_FORCE_FIXED_CHUNKSIZE=true;

	/** Manifest constant: Suppress leading whitespace.
	 * This should be used when normalize-to-SAX is called for the first chunk of a
	 * multi-chunk output, or one following unsuppressed whitespace in a previous
	 * chunk.
	 * @see #sendNormalizedSAXcharacters(org.xml.sax.ContentHandler,int,int)
	 */
	public static final int SUPPRESS_LEADING_WS=0x01;

	/** Manifest constant: Suppress trailing whitespace.
	 * This should be used when normalize-to-SAX is called for the last chunk of a
	 * multi-chunk output; it may have to be or'ed with SUPPRESS_LEADING_WS.
	 */
	public static final int SUPPRESS_TRAILING_WS=0x02;

	/** Manifest constant: Suppress both leading and trailing whitespace.
	 * This should be used when normalize-to-SAX is called for a complete string.
	 * (I'm not wild about the name of this one. Ideas welcome.)
	 * @see #sendNormalizedSAXcharacters(org.xml.sax.ContentHandler,int,int)
	 */
	public static final int SUPPRESS_BOTH
		= SUPPRESS_LEADING_WS | SUPPRESS_TRAILING_WS;

	/** Manifest constant: Carry trailing whitespace of one chunk as leading
	 * whitespace of the next chunk. Used internally; I don't see any reason
	 * to make it public right now.
	 */
	private static final int CARRY_WS=0x04;

	/**
   * Field m_chunkBits sets our chunking strategy, by saying how many
   * bits of index can be used within a single chunk before flowing over
   * to the next chunk. For example, if m_chunkbits is set to 15, each
   * chunk can contain up to 2^15 (32K) characters
   */
  int m_chunkBits = 15;

  /**
   * Field m_maxChunkBits affects our chunk-growth strategy, by saying what
   * the largest permissible chunk size is in this particular FastStringBuffer
   * hierarchy.
   */
  int m_maxChunkBits = 15;

  /**
   * Field m_rechunkBits affects our chunk-growth strategy, by saying how
   * many chunks should be allocated at one size before we encapsulate them
   * into the first chunk of the next size up. For example, if m_rechunkBits
   * is set to 3, then after 8 chunks at a given size we will rebundle
   * them as the first element of a FastStringBuffer using a chunk size
   * 8 times larger (chunkBits shifted left three bits).
   */
  int m_rebundleBits = 2;

  /**
   * Field m_chunkSize establishes the maximum size of one chunk of the array
   * as 2**chunkbits characters.
   * (Which may also be the minimum size if we aren't tuning for storage)
   */
  int m_chunkSize;  // =1<<(m_chunkBits-1);

  /**
   * Field m_chunkMask is m_chunkSize-1 -- in other words, m_chunkBits
   * worth of low-order '1' bits, useful for shift-and-mask addressing
   * within the chunks.
   */
  int m_chunkMask;  // =m_chunkSize-1;

  /**
   * Field m_array holds the string buffer's text contents, using an
   * array-of-arrays. Note that this array, and the arrays it contains, may be
   * reallocated when necessary in order to allow the buffer to grow;
   * references to them should be considered to be invalidated after any
   * append. However, the only time these arrays are directly exposed
   * is in the sendSAXcharacters call.
   */
  char[][] m_array;

  /**
   * Field m_lastChunk is an index into m_array[], pointing to the last
   * chunk of the Chunked Array currently in use. Note that additional
   * chunks may actually be allocated, eg if the FastStringBuffer had
   * previously been truncated or if someone issued an ensureSpace request.
   * <p>
   * The insertion point for append operations is addressed by the combination
   * of m_lastChunk and m_firstFree.
   */
  int m_lastChunk = 0;

  /**
   * Field m_firstFree is an index into m_array[m_lastChunk][], pointing to
   * the first character in the Chunked Array which is not part of the
   * FastStringBuffer's current content. Since m_array[][] is zero-based,
   * the length of that content can be calculated as
   * (m_lastChunk<<m_chunkBits) + m_firstFree
   */
  int m_firstFree = 0;

  /**
   * Field m_innerFSB, when non-null, is a FastStringBuffer whose total
   * length equals m_chunkSize, and which replaces m_array[0]. This allows
   * building a hierarchy of FastStringBuffers, where early appends use
   * a smaller chunkSize (for less wasted memory overhead) but later
   * ones use a larger chunkSize (for less heap activity overhead).
   */
  FastStringBuffer m_innerFSB = null;

  /**
   * Construct a FastStringBuffer, with allocation policy as per parameters.
   * <p>
   * For coding convenience, I've expressed both allocation sizes in terms of
   * a number of bits. That's needed for the final size of a chunk,
   * to permit fast and efficient shift-and-mask addressing. It's less critical
   * for the inital size, and may be reconsidered.
   * <p>
   * An alternative would be to accept integer sizes and round to powers of two;
   * that really doesn't seem to buy us much, if anything.
   *
   * @param initChunkBits Length in characters of the initial allocation
   * of a chunk, expressed in log-base-2. (That is, 10 means allocate 1024
   * characters.) Later chunks will use larger allocation units, to trade off
   * allocation speed of large document against storage efficiency of small
   * ones.
   * @param maxChunkBits Number of character-offset bits that should be used for
   * addressing within a chunk. Maximum length of a chunk is 2^chunkBits
   * characters.
   * @param rebundleBits Number of character-offset bits that addressing should
   * advance before we attempt to take a step from initChunkBits to maxChunkBits
   */
  public FastStringBuffer(int initChunkBits, int maxChunkBits,
                          int rebundleBits)
  {
    if(DEBUG_FORCE_INIT_BITS!=0) initChunkBits=DEBUG_FORCE_INIT_BITS;

    // %REVIEW%
    // Should this force to larger value, or smaller? Smaller less efficient, but if
    // someone requested variable mode it's because they care about storage space.
    // On the other hand, given the other changes I'm making, odds are that we should
    // adopt the larger size. Dither, dither, dither... This is just stopgap workaround
    // anyway; we need a permanant solution.
    //
    if(DEBUG_FORCE_FIXED_CHUNKSIZE) maxChunkBits=initChunkBits;
    //if(DEBUG_FORCE_FIXED_CHUNKSIZE) initChunkBits=maxChunkBits;

    m_array = new char[16][];

    // Don't bite off more than we're prepared to swallow!
    if (initChunkBits > maxChunkBits)
      initChunkBits = maxChunkBits;

    m_chunkBits = initChunkBits;
    m_maxChunkBits = maxChunkBits;
    m_rebundleBits = rebundleBits;
    m_chunkSize = 1 << (initChunkBits);
    m_chunkMask = m_chunkSize - 1;
    m_array[0] = new char[m_chunkSize];
  }

  /**
   * Construct a FastStringBuffer, using a default rebundleBits value.
   *
   * NEEDSDOC @param initChunkBits
   * NEEDSDOC @param maxChunkBits
   */
  public FastStringBuffer(int initChunkBits, int maxChunkBits)
  {
    this(initChunkBits, maxChunkBits, 2);
  }

  /**
   * Construct a FastStringBuffer, using default maxChunkBits and
   * rebundleBits values.
   * <p>
   * ISSUE: Should this call assert initial size, or fixed size?
   * Now configured as initial, with a default for fixed.
   *
   * NEEDSDOC @param initChunkBits
   */
  public FastStringBuffer(int initChunkBits)
  {
    this(initChunkBits, 15, 2);
  }

  /**
   * Construct a FastStringBuffer, using a default allocation policy.
   */
  public FastStringBuffer()
  {

    // 10 bits is 1K. 15 bits is 32K. Remember that these are character
    // counts, so actual memory allocation unit is doubled for UTF-16 chars.
    //
    // For reference: In the original FastStringBuffer, we simply
    // overallocated by blocksize (default 1KB) on each buffer-growth.
    this(10, 15, 2);
  }

  /**
   * Get the length of the list. Synonym for length().
   *
   * @return the number of characters in the FastStringBuffer's content.
   */
  public final int size()
  {
    return (m_lastChunk << m_chunkBits) + m_firstFree;
  }

  /**
   * Get the length of the list. Synonym for size().
   *
   * @return the number of characters in the FastStringBuffer's content.
   */
  public final int length()
  {
    return (m_lastChunk << m_chunkBits) + m_firstFree;
  }

  /**
   * Discard the content of the FastStringBuffer, and most of the memory
   * that was allocated by it, restoring the initial state. Note that this
   * may eventually be different from setLength(0), which see.
   */
  public final void reset()
  {

    m_lastChunk = 0;
    m_firstFree = 0;

    // Recover the original chunk size
    FastStringBuffer innermost = this;

    while (innermost.m_innerFSB != null)
    {
      innermost = innermost.m_innerFSB;
    }

    m_chunkBits = innermost.m_chunkBits;
    m_chunkSize = innermost.m_chunkSize;
    m_chunkMask = innermost.m_chunkMask;

    // Discard the hierarchy
    m_innerFSB = null;
    m_array = new char[16][0];
    m_array[0] = new char[m_chunkSize];
  }

  /**
   * Directly set how much of the FastStringBuffer's storage is to be
   * considered part of its content. This is a fast but hazardous
   * operation. It is not protected against negative values, or values
   * greater than the amount of storage currently available... and even
   * if additional storage does exist, its contents are unpredictable.
   * The only safe use for our setLength() is to truncate the FastStringBuffer
   * to a shorter string.
   *
   * @param l New length. If l<0 or l>=getLength(), this operation will
   * not report an error but future operations will almost certainly fail.
   */
  public final void setLength(int l)
  {
    m_lastChunk = l >>> m_chunkBits;

    if (m_lastChunk == 0 && m_innerFSB != null)
    {
      // Replace this FSB with the appropriate inner FSB, truncated
      m_innerFSB.setLength(l, this);
    }
    else
    {
      m_firstFree = l & m_chunkMask;

	  // There's an edge case if l is an exact multiple of m_chunkBits, which risks leaving
	  // us pointing at the start of a chunk which has not yet been allocated. Rather than
	  // pay the cost of dealing with that in the append loops (more scattered and more
	  // inner-loop), we correct it here by moving to the safe side of that
	  // line -- as we would have left the indexes had we appended up to that point.
      if(m_firstFree==0 && m_lastChunk>0)
      {
      	--m_lastChunk;
      	m_firstFree=m_chunkSize;
      }
    }
  }

  /**
   * Subroutine for the public setLength() method. Deals with the fact
   * that truncation may require restoring one of the innerFSBs
   *
   * NEEDSDOC @param l
   * NEEDSDOC @param rootFSB
   */
  private final void setLength(int l, FastStringBuffer rootFSB)
  {

    m_lastChunk = l >>> m_chunkBits;

    if (m_lastChunk == 0 && m_innerFSB != null)
    {
      m_innerFSB.setLength(l, rootFSB);
    }
    else
    {

      // Undo encapsulation -- pop the innerFSB data back up to root.
      // Inefficient, but attempts to keep the code simple.
      rootFSB.m_chunkBits = m_chunkBits;
      rootFSB.m_maxChunkBits = m_maxChunkBits;
      rootFSB.m_rebundleBits = m_rebundleBits;
      rootFSB.m_chunkSize = m_chunkSize;
      rootFSB.m_chunkMask = m_chunkMask;
      rootFSB.m_array = m_array;
      rootFSB.m_innerFSB = m_innerFSB;
      rootFSB.m_lastChunk = m_lastChunk;

      // Finally, truncate this sucker.
      rootFSB.m_firstFree = l & m_chunkMask;
    }
  }

  /**
   * Note that this operation has been somewhat deoptimized by the shift to a
   * chunked array, as there is no factory method to produce a String object
   * directly from an array of arrays and hence a double copy is needed.
   * By using ensureCapacity we hope to minimize the heap overhead of building
   * the intermediate StringBuffer.
   * <p>
   * (It really is a pity that Java didn't design String as a final subclass
   * of MutableString, rather than having StringBuffer be a separate hierarchy.
   * We'd avoid a <strong>lot</strong> of double-buffering.)
   *
   * @return the contents of the FastStringBuffer as a standard Java string.
   */
  public final String toString()
  {

    int length = (m_lastChunk << m_chunkBits) + m_firstFree;

    return getString(new StringBuffer(length), 0, 0, length).toString();
  }

  /**
   * Append a single character onto the FastStringBuffer, growing the
   * storage if necessary.
   * <p>
   * NOTE THAT after calling append(), previously obtained
   * references to m_array[][] may no longer be valid....
   * though in fact they should be in this instance.
   *
   * @param value character to be appended.
   */
  public final void append(char value)
  {

    char[] chunk;

    // We may have preallocated chunks. If so, all but last should
    // be at full size.

    if (m_firstFree < m_chunkSize)  // Simplified test single-character-fits
      chunk = m_array[m_lastChunk];
    else
    {

      // Extend array?
      int i = m_array.length;

      if (m_lastChunk + 1 == i)
      {
        char[][] newarray = new char[i + 16][];

        System.arraycopy(m_array, 0, newarray, 0, i);

        m_array = newarray;
      }

      // Advance one chunk
      chunk = m_array[++m_lastChunk];

      if (chunk == null)
      {

        // Hierarchical encapsulation
        if (m_lastChunk == 1 << m_rebundleBits
                && m_chunkBits < m_maxChunkBits)
        {

          // Should do all the work of both encapsulating
          // existing data and establishing new sizes/offsets
          m_innerFSB = new FastStringBuffer(this);
        }

        // Add a chunk.
        chunk = m_array[m_lastChunk] = new char[m_chunkSize];
      }

      m_firstFree = 0;
    }

    // Space exists in the chunk. Append the character.
    chunk[m_firstFree++] = value;
  }

  /**
   * Append the contents of a String onto the FastStringBuffer,
   * growing the storage if necessary.
   * <p>
   * NOTE THAT after calling append(), previously obtained
   * references to m_array[] may no longer be valid.
   *
   * @param value String whose contents are to be appended.
   */
  public final void append(String value)
  {

    if (value == null)
      return;
    int strlen = value.length();

    if (0 == strlen)
      return;

    int copyfrom = 0;
    char[] chunk = m_array[m_lastChunk];
    int available = m_chunkSize - m_firstFree;

    // Repeat while data remains to be copied
    while (strlen > 0)
    {

      // Copy what fits
      if (available > strlen)
        available = strlen;

      value.getChars(copyfrom, copyfrom + available, m_array[m_lastChunk],
                     m_firstFree);

      strlen -= available;
      copyfrom += available;

      // If there's more left, allocate another chunk and continue
      if (strlen > 0)
      {

        // Extend array?
        int i = m_array.length;

        if (m_lastChunk + 1 == i)
        {
          char[][] newarray = new char[i + 16][];

          System.arraycopy(m_array, 0, newarray, 0, i);

          m_array = newarray;
        }

        // Advance one chunk
        chunk = m_array[++m_lastChunk];

        if (chunk == null)
        {

          // Hierarchical encapsulation
          if (m_lastChunk == 1 << m_rebundleBits
                  && m_chunkBits < m_maxChunkBits)
          {

            // Should do all the work of both encapsulating
            // existing data and establishing new sizes/offsets
            m_innerFSB = new FastStringBuffer(this);
          }

          // Add a chunk.
          chunk = m_array[m_lastChunk] = new char[m_chunkSize];
        }

        available = m_chunkSize;
        m_firstFree = 0;
      }
    }

    // Adjust the insert point in the last chunk, when we've reached it.
    m_firstFree += available;
  }

  /**
   * Append the contents of a StringBuffer onto the FastStringBuffer,
   * growing the storage if necessary.
   * <p>
   * NOTE THAT after calling append(), previously obtained
   * references to m_array[] may no longer be valid.
   *
   * @param value StringBuffer whose contents are to be appended.
   */
  public final void append(StringBuffer value)
  {

    if (value == null)
      return;
    int strlen = value.length();

    if (0 == strlen)
      return;

    int copyfrom = 0;
    char[] chunk = m_array[m_lastChunk];
    int available = m_chunkSize - m_firstFree;

    // Repeat while data remains to be copied
    while (strlen > 0)
    {

      // Copy what fits
      if (available > strlen)
        available = strlen;

      value.getChars(copyfrom, copyfrom + available, m_array[m_lastChunk],
                     m_firstFree);

      strlen -= available;
      copyfrom += available;

      // If there's more left, allocate another chunk and continue
      if (strlen > 0)
      {

        // Extend array?
        int i = m_array.length;

        if (m_lastChunk + 1 == i)
        {
          char[][] newarray = new char[i + 16][];

          System.arraycopy(m_array, 0, newarray, 0, i);

          m_array = newarray;
        }

        // Advance one chunk
        chunk = m_array[++m_lastChunk];

        if (chunk == null)
        {

          // Hierarchical encapsulation
          if (m_lastChunk == 1 << m_rebundleBits
                  && m_chunkBits < m_maxChunkBits)
          {

            // Should do all the work of both encapsulating
            // existing data and establishing new sizes/offsets
            m_innerFSB = new FastStringBuffer(this);
          }

          // Add a chunk.
          chunk = m_array[m_lastChunk] = new char[m_chunkSize];
        }

        available = m_chunkSize;
        m_firstFree = 0;
      }
    }

    // Adjust the insert point in the last chunk, when we've reached it.
    m_firstFree += available;
  }

  /**
   * Append part of the contents of a Character Array onto the
   * FastStringBuffer,  growing the storage if necessary.
   * <p>
   * NOTE THAT after calling append(), previously obtained
   * references to m_array[] may no longer be valid.
   *
   * @param chars character array from which data is to be copied
   * @param start offset in chars of first character to be copied,
   * zero-based.
   * @param length number of characters to be copied
   */
  public final void append(char[] chars, int start, int length)
  {

    int strlen = length;

    if (0 == strlen)
      return;

    int copyfrom = start;
    char[] chunk = m_array[m_lastChunk];
    int available = m_chunkSize - m_firstFree;

    // Repeat while data remains to be copied
    while (strlen > 0)
    {

      // Copy what fits
      if (available > strlen)
        available = strlen;

      System.arraycopy(chars, copyfrom, m_array[m_lastChunk], m_firstFree,
                       available);

      strlen -= available;
      copyfrom += available;

      // If there's more left, allocate another chunk and continue
      if (strlen > 0)
      {

        // Extend array?
        int i = m_array.length;

        if (m_lastChunk + 1 == i)
        {
          char[][] newarray = new char[i + 16][];

          System.arraycopy(m_array, 0, newarray, 0, i);

          m_array = newarray;
        }

        // Advance one chunk
        chunk = m_array[++m_lastChunk];

        if (chunk == null)
        {

          // Hierarchical encapsulation
          if (m_lastChunk == 1 << m_rebundleBits
                  && m_chunkBits < m_maxChunkBits)
          {

            // Should do all the work of both encapsulating
            // existing data and establishing new sizes/offsets
            m_innerFSB = new FastStringBuffer(this);
          }

          // Add a chunk.
          chunk = m_array[m_lastChunk] = new char[m_chunkSize];
        }

        available = m_chunkSize;
        m_firstFree = 0;
      }
    }

    // Adjust the insert point in the last chunk, when we've reached it.
    m_firstFree += available;
  }

  /**
   * Append the contents of another FastStringBuffer onto
   * this FastStringBuffer, growing the storage if necessary.
   * <p>
   * NOTE THAT after calling append(), previously obtained
   * references to m_array[] may no longer be valid.
   *
   * @param value FastStringBuffer whose contents are
   * to be appended.
   */
  public final void append(FastStringBuffer value)
  {

    // Complicating factor here is that the two buffers may use
    // different chunk sizes, and even if they're the same we're
    // probably on a different alignment due to previously appended
    // data. We have to work through the source in bite-sized chunks.
    if (value == null)
      return;
    int strlen = value.length();

    if (0 == strlen)
      return;

    int copyfrom = 0;
    char[] chunk = m_array[m_lastChunk];
    int available = m_chunkSize - m_firstFree;

    // Repeat while data remains to be copied
    while (strlen > 0)
    {

      // Copy what fits
      if (available > strlen)
        available = strlen;

      int sourcechunk = (copyfrom + value.m_chunkSize - 1)
                        >>> value.m_chunkBits;
      int sourcecolumn = copyfrom & value.m_chunkMask;
      int runlength = value.m_chunkSize - sourcecolumn;

      if (runlength > available)
        runlength = available;

      System.arraycopy(value.m_array[sourcechunk], sourcecolumn,
                       m_array[m_lastChunk], m_firstFree, runlength);

      if (runlength != available)
        System.arraycopy(value.m_array[sourcechunk + 1], 0,
                         m_array[m_lastChunk], m_firstFree + runlength,
                         available - runlength);

      strlen -= available;
      copyfrom += available;

      // If there's more left, allocate another chunk and continue
      if (strlen > 0)
      {

        // Extend array?
        int i = m_array.length;

        if (m_lastChunk + 1 == i)
        {
          char[][] newarray = new char[i + 16][];

          System.arraycopy(m_array, 0, newarray, 0, i);

          m_array = newarray;
        }

        // Advance one chunk
        chunk = m_array[++m_lastChunk];

        if (chunk == null)
        {

          // Hierarchical encapsulation
          if (m_lastChunk == 1 << m_rebundleBits
                  && m_chunkBits < m_maxChunkBits)
          {

            // Should do all the work of both encapsulating
            // existing data and establishing new sizes/offsets
            m_innerFSB = new FastStringBuffer(this);
          }

          // Add a chunk.
          chunk = m_array[m_lastChunk] = new char[m_chunkSize];
        }

        available = m_chunkSize;
        m_firstFree = 0;
      }
    }

    // Adjust the insert point in the last chunk, when we've reached it.
    m_firstFree += available;
  }

  /**
   * @return true if the specified range of characters are all whitespace,
   * as defined by XMLCharacterRecognizer.
   * <p>
   * CURRENTLY DOES NOT CHECK FOR OUT-OF-RANGE.
   *
   * @param start Offset of first character in the range.
   * @param length Number of characters to send.
   */
  public boolean isWhitespace(int start, int length)
  {

    int sourcechunk = start >>> m_chunkBits;
    int sourcecolumn = start & m_chunkMask;
    int available = m_chunkSize - sourcecolumn;
    boolean chunkOK;

    while (length > 0)
    {
      int runlength = (length <= available) ? length : available;

      if (sourcechunk == 0 && m_innerFSB != null)
        chunkOK = m_innerFSB.isWhitespace(sourcecolumn, runlength);
      else
        chunkOK = org.apache.xml.utils.XMLCharacterRecognizer.isWhiteSpace(
          m_array[sourcechunk], sourcecolumn, runlength);

      if (!chunkOK)
        return false;

      length -= runlength;

      ++sourcechunk;

      sourcecolumn = 0;
      available = m_chunkSize;
    }

    return true;
  }

  /**
   * @param start Offset of first character in the range.
   * @param length Number of characters to send.
   * @return a new String object initialized from the specified range of
   * characters.
   */
  public String getString(int start, int length)
  {
    int startColumn = start & m_chunkMask;
    int startChunk = start >>> m_chunkBits;
    if (startColumn + length < m_chunkMask && m_innerFSB == null) {
      return getOneChunkString(startChunk, startColumn, length);
    }
    return getString(new StringBuffer(length), startChunk, startColumn,
                     length).toString();
  }

  protected String getOneChunkString(int startChunk, int startColumn,
                                     int length) {
    return new String(m_array[startChunk], startColumn, length);
  }

  /**
   * @param sb StringBuffer to be appended to
   * @param start Offset of first character in the range.
   * @param length Number of characters to send.
   * @return sb with the requested text appended to it
   */
  StringBuffer getString(StringBuffer sb, int start, int length)
  {
    return getString(sb, start >>> m_chunkBits, start & m_chunkMask, length);
  }

  /**
   * Internal support for toString() and getString().
   * PLEASE NOTE SIGNATURE CHANGE from earlier versions; it now appends into
   * and returns a StringBuffer supplied by the caller. This simplifies
   * m_innerFSB support.
   * <p>
   * Note that this operation has been somewhat deoptimized by the shift to a
   * chunked array, as there is no factory method to produce a String object
   * directly from an array of arrays and hence a double copy is needed.
   * By presetting length we hope to minimize the heap overhead of building
   * the intermediate StringBuffer.
   * <p>
   * (It really is a pity that Java didn't design String as a final subclass
   * of MutableString, rather than having StringBuffer be a separate hierarchy.
   * We'd avoid a <strong>lot</strong> of double-buffering.)
   *
   *
   * @param sb
   * @param startChunk
   * @param startColumn
   * @param length
   *
   * @return the contents of the FastStringBuffer as a standard Java string.
   */
  StringBuffer getString(StringBuffer sb, int startChunk, int startColumn,
                         int length)
  {

    int stop = (startChunk << m_chunkBits) + startColumn + length;
    int stopChunk = stop >>> m_chunkBits;
    int stopColumn = stop & m_chunkMask;

    // Factored out
    //StringBuffer sb=new StringBuffer(length);
    for (int i = startChunk; i < stopChunk; ++i)
    {
      if (i == 0 && m_innerFSB != null)
        m_innerFSB.getString(sb, startColumn, m_chunkSize - startColumn);
      else
        sb.append(m_array[i], startColumn, m_chunkSize - startColumn);

      startColumn = 0;  // after first chunk
    }

    if (stopChunk == 0 && m_innerFSB != null)
      m_innerFSB.getString(sb, startColumn, stopColumn - startColumn);
    else if (stopColumn > startColumn)
      sb.append(m_array[stopChunk], startColumn, stopColumn - startColumn);

    return sb;
  }

  /**
   * Get a single character from the string buffer.
   *
   *
   * @param pos character position requested.
   * @return A character from the requested position.
   */
  public char charAt(int pos)
  {
    int startChunk = pos >>> m_chunkBits;

    if (startChunk == 0 && m_innerFSB != null)
      return m_innerFSB.charAt(pos & m_chunkMask);
    else
      return m_array[startChunk][pos & m_chunkMask];
  }

  /**
   * Sends the specified range of characters as one or more SAX characters()
   * events.
   * Note that the buffer reference passed to the ContentHandler may be
   * invalidated if the FastStringBuffer is edited; it's the user's
   * responsibility to manage access to the FastStringBuffer to prevent this
   * problem from arising.
   * <p>
   * Note too that there is no promise that the output will be sent as a
   * single call. As is always true in SAX, one logical string may be split
   * across multiple blocks of memory and hence delivered as several
   * successive events.
   *
   * @param ch SAX ContentHandler object to receive the event.
   * @param start Offset of first character in the range.
   * @param length Number of characters to send.
   * @exception org.xml.sax.SAXException may be thrown by handler's
   * characters() method.
   */
  public void sendSAXcharacters(
          org.xml.sax.ContentHandler ch, int start, int length)
            throws org.xml.sax.SAXException
  {

    int startChunk = start >>> m_chunkBits;
    int startColumn = start & m_chunkMask;
    if (startColumn + length < m_chunkMask && m_innerFSB == null) {
        ch.characters(m_array[startChunk], startColumn, length);
        return;
    }

    int stop = start + length;
    int stopChunk = stop >>> m_chunkBits;
    int stopColumn = stop & m_chunkMask;

    for (int i = startChunk; i < stopChunk; ++i)
    {
      if (i == 0 && m_innerFSB != null)
        m_innerFSB.sendSAXcharacters(ch, startColumn,
                                     m_chunkSize - startColumn);
      else
        ch.characters(m_array[i], startColumn, m_chunkSize - startColumn);

      startColumn = 0;  // after first chunk
    }

    // Last, or only, chunk
    if (stopChunk == 0 && m_innerFSB != null)
      m_innerFSB.sendSAXcharacters(ch, startColumn, stopColumn - startColumn);
    else if (stopColumn > startColumn)
    {
      ch.characters(m_array[stopChunk], startColumn,
                    stopColumn - startColumn);
    }
  }

  /**
   * Sends the specified range of characters as one or more SAX characters()
   * events, normalizing the characters according to XSLT rules.
   *
   * @param ch SAX ContentHandler object to receive the event.
   * @param start Offset of first character in the range.
   * @param length Number of characters to send.
   * @return normalization status to apply to next chunk (because we may
   * have been called recursively to process an inner FSB):
   * <dl>
   * <dt>0</dt>
   * <dd>if this output did not end in retained whitespace, and thus whitespace
   * at the start of the following chunk (if any) should be converted to a
   * single space.
   * <dt>SUPPRESS_LEADING_WS</dt>
   * <dd>if this output ended in retained whitespace, and thus whitespace
   * at the start of the following chunk (if any) should be completely
   * suppressed.</dd>
   * </dd>
   * </dl>
   * @exception org.xml.sax.SAXException may be thrown by handler's
   * characters() method.
   */
  public int sendNormalizedSAXcharacters(
          org.xml.sax.ContentHandler ch, int start, int length)
            throws org.xml.sax.SAXException
  {
	// This call always starts at the beginning of the
    // string being written out, either because it was called directly or
    // because it was an m_innerFSB recursion. This is important since
	// it gives us a well-known initial state for this flag:
	int stateForNextChunk=SUPPRESS_LEADING_WS;

    int stop = start + length;
    int startChunk = start >>> m_chunkBits;
    int startColumn = start & m_chunkMask;
    int stopChunk = stop >>> m_chunkBits;
    int stopColumn = stop & m_chunkMask;

    for (int i = startChunk; i < stopChunk; ++i)
    {
      if (i == 0 && m_innerFSB != null)
				stateForNextChunk=
        m_innerFSB.sendNormalizedSAXcharacters(ch, startColumn,
                                     m_chunkSize - startColumn);
      else
				stateForNextChunk=
        sendNormalizedSAXcharacters(m_array[i], startColumn,
                                    m_chunkSize - startColumn,
																		ch,stateForNextChunk);

      startColumn = 0;  // after first chunk
    }

    // Last, or only, chunk
    if (stopChunk == 0 && m_innerFSB != null)
			stateForNextChunk= // %REVIEW% Is this update really needed?
      m_innerFSB.sendNormalizedSAXcharacters(ch, startColumn, stopColumn - startColumn);
    else if (stopColumn > startColumn)
    {
			stateForNextChunk= // %REVIEW% Is this update really needed?
      sendNormalizedSAXcharacters(m_array[stopChunk],
																	startColumn, stopColumn - startColumn,
																	ch, stateForNextChunk | SUPPRESS_TRAILING_WS);
    }
		return stateForNextChunk;
  }

  static final char[] SINGLE_SPACE = {' '};

  /**
   * Internal method to directly normalize and dispatch the character array.
   * This version is aware of the fact that it may be called several times
   * in succession if the data is made up of multiple "chunks", and thus
   * must actively manage the handling of leading and trailing whitespace.
   *
   * Note: The recursion is due to the possible recursion of inner FSBs.
   *
   * @param ch The characters from the XML document.
   * @param start The start position in the array.
   * @param length The number of characters to read from the array.
   * @param handler SAX ContentHandler object to receive the event.
   * @param edgeTreatmentFlags How leading/trailing spaces should be handled.
   * This is a bitfield contining two flags, bitwise-ORed together:
   * <dl>
   * <dt>SUPPRESS_LEADING_WS</dt>
   * <dd>When false, causes leading whitespace to be converted to a single
   * space; when true, causes it to be discarded entirely.
   * Should be set TRUE for the first chunk, and (in multi-chunk output)
   * whenever the previous chunk ended in retained whitespace.</dd>
   * <dt>SUPPRESS_TRAILING_WS</dt>
   * <dd>When false, causes trailing whitespace to be converted to a single
   * space; when true, causes it to be discarded entirely.
   * Should be set TRUE for the last or only chunk.
   * </dd>
   * </dl>
   * @return normalization status, as in the edgeTreatmentFlags parameter:
   * <dl>
   * <dt>0</dt>
   * <dd>if this output did not end in retained whitespace, and thus whitespace
   * at the start of the following chunk (if any) should be converted to a
   * single space.
   * <dt>SUPPRESS_LEADING_WS</dt>
   * <dd>if this output ended in retained whitespace, and thus whitespace
   * at the start of the following chunk (if any) should be completely
   * suppressed.</dd>
   * </dd>
   * </dl>
   *
   *
   * @exception org.xml.sax.SAXException Any SAX exception, possibly
   *            wrapping another exception.
   */
  static int sendNormalizedSAXcharacters(char ch[],
             int start, int length,
             org.xml.sax.ContentHandler handler,
						 int edgeTreatmentFlags)
          throws org.xml.sax.SAXException
  {
     boolean processingLeadingWhitespace =
                       ((edgeTreatmentFlags & SUPPRESS_LEADING_WS) != 0);
     boolean seenWhitespace = ((edgeTreatmentFlags & CARRY_WS) != 0);
     int currPos = start;
     int limit = start+length;

     // Strip any leading spaces first, if required
     if (processingLeadingWhitespace) {
         for (; currPos < limit
                && XMLCharacterRecognizer.isWhiteSpace(ch[currPos]);
              currPos++) { }

         // If we've only encountered leading spaces, the
         // current state remains unchanged
         if (currPos == limit) {
             return edgeTreatmentFlags;
         }
     }

     // If we get here, there are no more leading spaces to strip
     while (currPos < limit) {
         int startNonWhitespace = currPos;

         // Grab a chunk of non-whitespace characters
         for (; currPos < limit
                && !XMLCharacterRecognizer.isWhiteSpace(ch[currPos]);
              currPos++) { }

         // Non-whitespace seen - emit them, along with a single
         // space for any preceding whitespace characters
         if (startNonWhitespace != currPos) {
             if (seenWhitespace) {
                 handler.characters(SINGLE_SPACE, 0, 1);
                 seenWhitespace = false;
             }
             handler.characters(ch, startNonWhitespace,
                                currPos - startNonWhitespace);
         }

         int startWhitespace = currPos;

         // Consume any whitespace characters
         for (; currPos < limit
                && XMLCharacterRecognizer.isWhiteSpace(ch[currPos]);
              currPos++) { }

         if (startWhitespace != currPos) {
             seenWhitespace = true;
         }
     }

     return (seenWhitespace ? CARRY_WS : 0)
            | (edgeTreatmentFlags & SUPPRESS_TRAILING_WS);
  }

  /**
   * Directly normalize and dispatch the character array.
   *
   * @param ch The characters from the XML document.
   * @param start The start position in the array.
   * @param length The number of characters to read from the array.
   * @param handler SAX ContentHandler object to receive the event.
   * @exception org.xml.sax.SAXException Any SAX exception, possibly
   *            wrapping another exception.
   */
  public static void sendNormalizedSAXcharacters(char ch[],
             int start, int length,
             org.xml.sax.ContentHandler handler)
          throws org.xml.sax.SAXException
  {
		sendNormalizedSAXcharacters(ch, start, length,
             handler, SUPPRESS_BOTH);
	}

	/**
   * Sends the specified range of characters as sax Comment.
   * <p>
   * Note that, unlike sendSAXcharacters, this has to be done as a single
   * call to LexicalHandler#comment.
   *
   * @param ch SAX LexicalHandler object to receive the event.
   * @param start Offset of first character in the range.
   * @param length Number of characters to send.
   * @exception org.xml.sax.SAXException may be thrown by handler's
   * characters() method.
   */
  public void sendSAXComment(
          org.xml.sax.ext.LexicalHandler ch, int start, int length)
            throws org.xml.sax.SAXException
  {

    // %OPT% Do it this way for now...
    String comment = getString(start, length);
    ch.comment(comment.toCharArray(), 0, length);
  }

  /**
   * Copies characters from this string into the destination character
   * array.
   *
   * @param      srcBegin   index of the first character in the string
   *                        to copy.
   * @param      srcEnd     index after the last character in the string
   *                        to copy.
   * @param      dst        the destination array.
   * @param      dstBegin   the start offset in the destination array.
   * @exception IndexOutOfBoundsException If any of the following
   *            is true:
   *            <ul><li><code>srcBegin</code> is negative.
   *            <li><code>srcBegin</code> is greater than <code>srcEnd</code>
   *            <li><code>srcEnd</code> is greater than the length of this
   *                string
   *            <li><code>dstBegin</code> is negative
   *            <li><code>dstBegin+(srcEnd-srcBegin)</code> is larger than
   *                <code>dst.length</code></ul>
   * @exception NullPointerException if <code>dst</code> is <code>null</code>
   */
  private void getChars(int srcBegin, int srcEnd, char dst[], int dstBegin)
  {
    // %TBD% Joe needs to write this function.  Make public when implemented.
  }

  /**
   * Encapsulation c'tor. After this is called, the source FastStringBuffer
   * will be reset to use the new object as its m_innerFSB, and will have
   * had its chunk size reset appropriately. IT SHOULD NEVER BE CALLED
   * EXCEPT WHEN source.length()==1<<(source.m_chunkBits+source.m_rebundleBits)
   *
   * NEEDSDOC @param source
   */
  private FastStringBuffer(FastStringBuffer source)
  {

    // Copy existing information into new encapsulation
    m_chunkBits = source.m_chunkBits;
    m_maxChunkBits = source.m_maxChunkBits;
    m_rebundleBits = source.m_rebundleBits;
    m_chunkSize = source.m_chunkSize;
    m_chunkMask = source.m_chunkMask;
    m_array = source.m_array;
    m_innerFSB = source.m_innerFSB;

    // These have to be adjusted because we're calling just at the time
    // when we would be about to allocate another chunk
    m_lastChunk = source.m_lastChunk - 1;
    m_firstFree = source.m_chunkSize;

    // Establish capsule as the Inner FSB, reset chunk sizes/addressing
    source.m_array = new char[16][];
    source.m_innerFSB = this;

    // Since we encapsulated just as we were about to append another
    // chunk, return ready to create the chunk after the innerFSB
    // -- 1, not 0.
    source.m_lastChunk = 1;
    source.m_firstFree = 0;
    source.m_chunkBits += m_rebundleBits;
    source.m_chunkSize = 1 << (source.m_chunkBits);
    source.m_chunkMask = source.m_chunkSize - 1;
  }
}