Quelle zutil.h Sprache: C

/* zutil.h -- internal interface and configuration of the compression library
* Copyright (C) 1995-1998 Jean-loup Gailly.
* For conditions of distribution and use, see copyright notice in zlib.h
*/

/* WARNING: this file should *not* be used by applications. It is
   part of the implementation of the compression library and is
   subject to change. Applications should only use zlib.h.
*/

/* @(#) $Id: zutil.h,v 1.1 2000/01/01 03:32:23 davem Exp $ */

#ifndef _Z_UTIL_H
#define _Z_UTIL_H

#include <linux/zlib.h>
#include <linux/string.h>
#include <linux/kernel.h>

typedef unsigned char  uch;
typedef unsigned short ush;
typedef unsigned long  ulg;

        /* common constants */

#define STORED_BLOCK 0
#define STATIC_TREES 1
#define DYN_TREES    2
/* The three kinds of block type */

#define MIN_MATCH  3
#define MAX_MATCH  258
/* The minimum and maximum match lengths */

#define PRESET_DICT 0x20 /* preset dictionary flag in zlib header */

        /* target dependencies */

        /* Common defaults */

#ifndef OS_CODE
#  define OS_CODE  0x03  /* assume Unix */
#endif

         /* functions */

typedef uLong (*check_func) (uLong check, const Byte *buf,
           uInt len);

                        /* checksum functions */

#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,i)  {s1 += buf[i]; s2 += s1;}
#define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
#define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
#define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
#define DO16(buf)   DO8(buf,0); DO8(buf,8);

/* ========================================================================= */
/*
     Update a running Adler-32 checksum with the bytes buf[0..len-1] and
   return the updated checksum. If buf is NULL, this function returns
   the required initial value for the checksum.
   An Adler-32 checksum is almost as reliable as a CRC32 but can be computed
   much faster. Usage example:

     uLong adler = zlib_adler32(0L, NULL, 0);

     while (read_buffer(buffer, length) != EOF) {
       adler = zlib_adler32(adler, buffer, length);
     }
     if (adler != original_adler) error();
*/
static inline uLong zlib_adler32(uLong adler,
     const Byte *buf,
     uInt len)
{
    unsigned long s1 = adler & 0xffff;
    unsigned long s2 = (adler >> 16) & 0xffff;
    int k;

    if (buf == NULL) return 1L;

    while (len > 0) {
        k = len < NMAX ? len : NMAX;
        len -= k;
        while (k >= 16) {
            DO16(buf);
     buf += 16;
            k -= 16;
        }
        if (k != 0) do {
            s1 += *buf++;
     s2 += s1;
        } while (--k);
        s1 %= BASE;
        s2 %= BASE;
    }
    return (s2 << 16) | s1;
}

#endif /* _Z_UTIL_H */

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