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    1   /*
    2    * Copyright 2012 The Netty Project
    3    *
    4    * The Netty Project licenses this file to you under the Apache License,
    5    * version 2.0 (the "License"); you may not use this file except in compliance
    6    * with the License. You may obtain a copy of the License at:
    7    *
    8    *   http://www.apache.org/licenses/LICENSE-2.0
    9    *
    10   * Unless required by applicable law or agreed to in writing, software
    11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
    12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
    13   * License for the specific language governing permissions and limitations
    14   * under the License.
    15   */
    16  /*
    17  Copyright (c) 2000,2001,2002,2003 ymnk, JCraft,Inc. All rights reserved.
    18
    19  Redistribution and use in source and binary forms, with or without
    20  modification, are permitted provided that the following conditions are met:
    21
    22    1. Redistributions of source code must retain the above copyright notice,
    23       this list of conditions and the following disclaimer.
    24
    25    2. Redistributions in binary form must reproduce the above copyright
    26       notice, this list of conditions and the following disclaimer in
    27       the documentation and/or other materials provided with the distribution.
    28
    29    3. The names of the authors may not be used to endorse or promote products
    30       derived from this software without specific prior written permission.
    31
    32  THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES,
    33  INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
    34  FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL JCRAFT,
    35  INC. OR ANY CONTRIBUTORS TO THIS SOFTWARE BE LIABLE FOR ANY DIRECT, INDIRECT,
    36  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
    37  LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
    38  OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
    39  LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
    40  NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
    41  EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
    42   */
    43  /*
    44   * This program is based on zlib-1.1.3, so all credit should go authors
    45   * Jean-loup Gailly(jloup@gzip.org) and Mark Adler(madler@alumni.caltech.edu)
    46   * and contributors of zlib.
    47   */
    48
    49  package org.jboss.netty.util.internal.jzlib;
    50
    51  final class Adler32 {
    52
    53      // largest prime smaller than 65536
    54      private static final int BASE = 65521;
    55      // NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1
    56      private static final int NMAX = 5552;
    57
    58      static long adler32(long adler, byte[] buf, int index, int len) {
    59          if (buf == null) {
    60              return 1L;
    61          }
    62
    63          long s1 = adler & 0xffff;
    64          long s2 = adler >> 16 & 0xffff;
    65          int k;
    66
    67          while (len > 0) {
    68              k = len < NMAX? len : NMAX;
    69              len -= k;
    70              while (k >= 16) {
    71                  s1 += buf[index ++] & 0xff;
    72                  s2 += s1;
    73                  s1 += buf[index ++] & 0xff;
    74                  s2 += s1;
    75                  s1 += buf[index ++] & 0xff;
    76                  s2 += s1;
    77                  s1 += buf[index ++] & 0xff;
    78                  s2 += s1;
    79                  s1 += buf[index ++] & 0xff;
    80                  s2 += s1;
    81                  s1 += buf[index ++] & 0xff;
    82                  s2 += s1;
    83                  s1 += buf[index ++] & 0xff;
    84                  s2 += s1;
    85                  s1 += buf[index ++] & 0xff;
    86                  s2 += s1;
    87                  s1 += buf[index ++] & 0xff;
    88                  s2 += s1;
    89                  s1 += buf[index ++] & 0xff;
    90                  s2 += s1;
    91                  s1 += buf[index ++] & 0xff;
    92                  s2 += s1;
    93                  s1 += buf[index ++] & 0xff;
    94                  s2 += s1;
    95                  s1 += buf[index ++] & 0xff;
    96                  s2 += s1;
    97                  s1 += buf[index ++] & 0xff;
    98                  s2 += s1;
    99                  s1 += buf[index ++] & 0xff;
    100                 s2 += s1;
    101                 s1 += buf[index ++] & 0xff;
    102                 s2 += s1;
    103                 k -= 16;
    104             }
    105             if (k != 0) {
    106                 do {
    107                     s1 += buf[index ++] & 0xff;
    108                     s2 += s1;
    109                 } while (-- k != 0);
    110             }
    111             s1 %= BASE;
    112             s2 %= BASE;
    113         }
    114         return s2 << 16 | s1;
    115     }
    116
    117     private Adler32() {
    118         // Utility class
    119     }
    120 }