content: /*
   * Copyright (C) 1999-2019 Alibaba Group Holding Limited.
   * Copyright (c) 1994, 2009, Oracle and/or its affiliates. All Rights Reserved.
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License, version 2.0,
   * as published by the Free Software Foundation.
   *
   * This program is also distributed with certain software (including
   * but not limited to OpenSSL) that is licensed under separate terms,
   * as designated in a particular file or component or in included license
   * documentation.  The authors of MySQL hereby grant you an additional
   * permission to link the program and your derivative works with the
   * separately licensed software that they have included with MySQL.
   *
   * This program 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 General Public License, version 2.0, for more details.
   *
   * You should have received a copy of the GNU General Public License along with
   * this program; if not, write to the Free Software Foundation, Inc.,
   * 51 Franklin Street, Suite 500, Boston, MA 02110-1335 USA
   */
  package com.alibaba.innodb.java.reader.util;
  
  /**
   * Page level checksum algorithm, see <code>innodb_utility.c</code>
   * in innodb source code.
   *
   * @author xu.zx
   */
  public class Checksum {
  
    public static final long UT_HASH_RANDOM_MASK = 1463735687L;
  
    public static final long UT_HASH_RANDOM_MASK2 = 1653893711L;
  
    private static long fold(long n1, long n2) {
      return (((((n1 ^ n2 ^ UT_HASH_RANDOM_MASK2) << 8) + n1) ^ UT_HASH_RANDOM_MASK) + n2);
    }
  
    public static long getValue(byte[] bytes, int offset, int limit) {
      long fold = 0L;
      for (int i = offset; i < limit; i++) {
        fold = fold(fold, bytes[i] & 0xFFL);
      }
      return fold;
    }
  
  }
  