include/adler32.h

   1 /*
   2  * Original code from zlib: only stylistic changes have been made to the it.
   3  * The following copyright notice has been kept as desired by the authors.
   4  */
   5 /* zlib.h -- interface of the 'zlib' general purpose compression library
   6
   7   Copyright (C) 1995-2005 Jean-loup Gailly and Mark Adler
   8
   9   This software is provided 'as-is', without any express or implied
  10   warranty.  In no event will the authors be held liable for any damages
  11   arising from the use of this software.
  12
  13   Permission is granted to anyone to use this software for any purpose,
  14   including commercial applications, and to alter it and redistribute it
  15   freely, subject to the following restrictions:
  16
  17   1. The origin of this software must not be misrepresented; you must not
  18      claim that you wrote the original software. If you use this software
  19      in a product, an acknowledgment in the product documentation would be
  20      appreciated but is not required.
  21   2. Altered source versions must be plainly marked as such, and must not be
  22      misrepresented as being the original software.
  23   3. This notice may not be removed or altered from any source distribution.
  24
  25   Jean-loup Gailly        Mark Adler
  26   jloup@gzip.org          madler@alumni.caltech.edu
  27
  28
  29   The data format used by the zlib library is described by RFCs (Request for
  30   Comments) 1950 to 1952 in the files http://www.ietf.org/rfc/rfc1950.txt
  31   (zlib format), rfc1951.txt (deflate format) and rfc1952.txt (gzip format).
  32 */
  33 #ifndef __ADLER32_H__
  34 #define __ADLER32_H__
  35
  36 #include <stdio.h>
  37
  38 #define BASE 65521L /* largest prime smaller than 65536 */
  39 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
  40 #define NMAX 5552
  41
  42 #define DO1(buf,i)  {s1 += buf[i]; s2 += s1;}
  43 #define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
  44 #define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
  45 #define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
  46 #define DO16(buf)   DO8(buf,0); DO8(buf,8);
  47
  48 /*
  49  * Update a running Adler-32 checksum with the bytes buf[0..len-1] and
  50  * return the updated checksum. If buf is NULL, this function returns
  51  * the required initial value for the checksum.
  52  * An Adler-32 checksum is almost as reliable as a CRC32 but can be computed
  53  * much faster. Usage example:
  54  *
  55  *      unsigned long adler = adler32(0L, NULL, 0);
  56  *
  57  *      while (read_buffer(buffer, length) != EOF) {
  58  *      adler = adler32(adler, buffer, length);
  59  *      }
  60  *      if (adler != original_adler) error();
  61  */
  62 static inline unsigned long zlib_adler32(unsigned long adler,
  63                                          const unsigned char *buf,
  64                                          unsigned int len)
  65 {
  66         unsigned long s1 = adler & 0xffff;
  67         unsigned long s2 = (adler >> 16) & 0xffff;
  68         int k;
  69
  70         if (buf == NULL)
  71                 return 1L;
  72
  73         while (len > 0) {
  74                 k = len < NMAX ? len : NMAX;
  75                 len -= k;
  76                 while (k >= 16) {
  77                         DO16(buf);
  78                         buf += 16;
  79                         k -= 16;
  80                 }
  81                 if (k != 0) do {
  82                                 s1 += *buf++;
  83                                 s2 += s1;
  84                         } while (--k);
  85                 s1 %= BASE;
  86                 s2 %= BASE;
  87         }
  88         return (s2 << 16) | s1;
  89 }
  90
  91 #endif /*__ADLER32_H__ */