adler32.c
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上传日期:2007-01-04
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- /* adler32.c -- compute the Adler-32 checksum of a data stream
- * Copyright (C) 1995 Mark Adler
- * For conditions of distribution and use, see copyright notice in zlib.h
- */
- /* $Id: adler32.c,v 1.6 1995/05/03 17:27:08 jloup Exp $ */
- #include "zlib.h"
- #define BASE 65521L /* largest prime smaller than 65536 */
- #define NMAX 5552
- /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
- #define DO1(buf) {s1 += *buf++; s2 += s1;}
- #define DO2(buf) DO1(buf); DO1(buf);
- #define DO4(buf) DO2(buf); DO2(buf);
- #define DO8(buf) DO4(buf); DO4(buf);
- #define DO16(buf) DO8(buf); DO8(buf);
- /* ========================================================================= */
- uLong adler32(adler, buf, len)
- uLong adler;
- Bytef *buf;
- uInt len;
- {
- unsigned long s1 = adler & 0xffff;
- unsigned long s2 = (adler >> 16) & 0xffff;
- int k;
- if (buf == Z_NULL) return 1L;
- while (len > 0) {
- k = len < NMAX ? len : NMAX;
- len -= k;
- while (k >= 16) {
- DO16(buf);
- k -= 16;
- }
- if (k != 0) do {
- DO1(buf);
- } while (--k);
- s1 %= BASE;
- s2 %= BASE;
- }
- return (s2 << 16) | s1;
- }