src/zlib/adler32.c

   1 /* adler32.c -- compute the Adler-32 checksum of a data stream
   2  * Copyright (C) 1995-1998 Mark Adler
   3  * For conditions of distribution and use, see copyright notice in zlib.h
   4  */
   5
   6 /* @(#) $Id$ */
   7
   8 #include "../zlib/zlib.h"
   9
  10 #define BASE 65521L /* largest prime smaller than 65536 */
  11 #define NMAX 5552
  12 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
  13
  14 #define DO1(buf,i)  {s1 += buf[i]; s2 += s1;}
  15 #define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
  16 #define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
  17 #define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
  18 #define DO16(buf)   DO8(buf,0); DO8(buf,8);
  19
  20 /* ========================================================================= */
  21 #if defined(__VISAGECPP__) /* Visualage can't handle this antiquated interface */
  22 uLong ZEXPORT adler32 (uLong adler, const Bytef* buf, uInt len)
  23 #else
  24 uLong ZEXPORT adler32(adler, buf, len)
  25     uLong adler;
  26     const Bytef *buf;
  27     uInt len;
  28 #endif
  29 {
  30     unsigned long s1 = adler & 0xffff;
  31     unsigned long s2 = (adler >> 16) & 0xffff;
  32     int k;
  33
  34     if (buf == Z_NULL) return 1L;
  35
  36     while (len > 0) {
  37         k = len < NMAX ? len : NMAX;
  38         len -= k;
  39         while (k >= 16) {
  40             DO16(buf);
  41             buf += 16;
  42             k -= 16;
  43         }
  44         if (k != 0) do {
  45             s1 += *buf++;
  46             s2 += s1;
  47         } while (--k);
  48         s1 %= BASE;
  49         s2 %= BASE;
  50     }
  51     return (s2 << 16) | s1;
  52 }