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javaxdelta - Patch generator and patch tool using the GDIFF algorithm
There is a newer version: 1.5
/*
 *
 * Copyright (c) 2001 Torgeir Veimo
 * Copyright (c) 2002 Nicolas PERIDONT
 * Copyright (c) 2006 Heiko Klein
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */
package com.nothome.delta.text;

import java.io.IOException;
import java.nio.CharBuffer;
import java.util.HashMap;

/**
 * Checksum that uses character streams.
 */
public class Checksum {
  /** The checksums. */
  protected HashMap checksums = new HashMap();
  /** The Constant single_hash. */
  private static final char[] single_hash = com.nothome.delta.Checksum.getSingleHash();

  /**
   * Initialize checksums for source. The checksum for the chunkSize bytes at offset
   * chunkSize * i is inserted into an array at index i.
   *
   * @param source the source
   * @param chunkSize the chunk size
   * @throws IOException Signals that an I/O exception has occurred.
   */
  public Checksum(Readable source, int chunkSize) throws IOException {
    CharBuffer bb = CharBuffer.allocate(chunkSize * 2);
    int count = 0;
    while (true) {
      source.read(bb);
      bb.flip();
      if (bb.remaining() < chunkSize)
        break;
      while (bb.remaining() >= chunkSize) {
        long queryChecksum = queryChecksum0(bb, chunkSize);
        checksums.put(queryChecksum, count++);
      }
      bb.compact();
    }
  }

  /**
   * Marks, gets, then resets the checksum computed from the buffer.
   *
   * @param bb the bb
   * @param len the len
   * @return the long
   */
  public static long queryChecksum(CharBuffer bb, int len) {
    bb.mark();
    long sum = queryChecksum0(bb, len);
    bb.reset();
    return sum;
  }

  /**
   * B.
   *
   * @param c the c
   * @return the byte
   */
  private static byte b(char c) {
    return (byte) c;
  }

  /**
   * Query checksum0.
   *
   * @param bb the bb
   * @param len the len
   * @return the long
   */
  private static long queryChecksum0(CharBuffer bb, int len) {
    int high = 0;
    int low = 0;
    for (int i = 0; i < len; i++) {
      low += single_hash[b(bb.get()) + 128];
      high += low;
    }
    return ((high & 0xffff) << 16) | (low & 0xffff);
  }

  /**
   * Increment checksum.
   *
   * @param checksum the checksum
   * @param out the out
   * @param in the in
   * @param chunkSize the chunk size
   * @return the long
   */
  public static long incrementChecksum(long checksum, char out, char in, int chunkSize) {
    char old_c = single_hash[b(out) + 128];
    char new_c = single_hash[b(in) + 128];
    int low = ((int) ((checksum) & 0xffff) - old_c + new_c) & 0xffff;
    int high = ((int) ((checksum) >> 16) - (old_c * chunkSize) + low) & 0xffff;
    return (high << 16) | (low & 0xffff);
  }

  /**
   * Find checksum index.
   *
   * @param hashf the hashf
   * @return the int
   */
  public int findChecksumIndex(long hashf) {
    if (!checksums.containsKey(hashf))
      return -1;
    return checksums.get(hashf);
  }

  /**
   * Returns a debug String.
   *
   * @return the string
   */
  @Override
  public String toString() {
    return super.toString() + " checksums=" + this.checksums;
  }
}