1 /* adler32.c -- compute the Adler-32 checksum of a data stream 2 * Copyright (C) 1995-2002 Mark Adler 3 * For conditions of distribution and use, see copyright notice in zlib.h 4 */ 5 6 /* @(#) $Id$ */ 7 8 #include "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 ZEXPORT(uLong) adler32( /* adler, buf, len) */ 22 uLong adler, 23 const Bytef *buf, 24 uInt len ) 25 { 26 unsigned long s1 = adler & 0xffff; 27 unsigned long s2 = (adler >> 16) & 0xffff; 28 int k; 29 30 if (buf == Z_NULL) return 1L; 31 32 while (len > 0) { 33 k = len < NMAX ? len : NMAX; 34 len -= k; 35 while (k >= 16) { 36 DO16(buf); 37 buf += 16; 38 k -= 16; 39 } 40 if (k != 0) do { 41 s1 += *buf++; 42 s2 += s1; 43 } while (--k); 44 s1 %= BASE; 45 s2 %= BASE; 46 } 47 return (s2 << 16) | s1; 48 } 49
