SecurityServer/MacYarrow/zlib/adler32.c

   1 /*
   2  * Copyright (c) 2000-2001 Apple Computer, Inc. All Rights Reserved.
   3  *
   4  * The contents of this file constitute Original Code as defined in and are
   5  * subject to the Apple Public Source License Version 1.2 (the 'License').
   6  * You may not use this file except in compliance with the License. Please obtain
   7  * a copy of the License at http://www.apple.com/publicsource and read it before
   8  * using this file.
   9  *
  10  * This Original Code and all software distributed under the License are
  11  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESS
  12  * OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, INCLUDING WITHOUT
  13  * LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
  14  * PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. Please see the License for the
  15  * specific language governing rights and limitations under the License.
  16  */
  17
  18
  19 /* adler32.c -- compute the Adler-32 checksum of a data stream
  20  * Copyright (C) 1995-1998 Mark Adler
  21  * For conditions of distribution and use, see copyright notice in zlib.h
  22  */
  23
  24 /* @(#) $Id: adler32.c,v 1.1.1.1 2001/05/18 23:14:03 mb Exp $ */
  25
  26 #include "zlib.h"
  27
  28 #define BASE 65521L /* largest prime smaller than 65536 */
  29 #define NMAX 5552
  30 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
  31
  32 #define DO1(buf,i)  {s1 += buf[i]; s2 += s1;}
  33 #define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
  34 #define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
  35 #define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
  36 #define DO16(buf)   DO8(buf,0); DO8(buf,8);
  37
  38 /* ========================================================================= */
  39 uLong ZEXPORT adler32(adler, buf, len)
  40     uLong adler;
  41     const Bytef *buf;
  42     uInt len;
  43 {
  44     unsigned long s1 = adler & 0xffff;
  45     unsigned long s2 = (adler >> 16) & 0xffff;
  46     int k;
  47
  48     if (buf == Z_NULL) return 1L;
  49
  50     while (len > 0) {
  51         k = len < NMAX ? len : NMAX;
  52         len -= k;
  53         while (k >= 16) {
  54             DO16(buf);
  55             buf += 16;
  56             k -= 16;
  57         }
  58         if (k != 0) do {
  59             s1 += *buf++;
  60             s2 += s1;
  61         } while (--k);
  62         s1 %= BASE;
  63         s2 %= BASE;
  64     }
  65     return (s2 << 16) | s1;
  66 }