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zip_filerange_crc.c
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00001 /*
00002   zip_filerange_crc.c -- compute CRC32 for a range of a file
00003   Copyright (C) 2008-2009 Dieter Baron and Thomas Klausner
00004 
00005   This file is part of libzip, a library to manipulate ZIP archives.
00006   The authors can be contacted at <libzip@nih.at>
00007 
00008   Redistribution and use in source and binary forms, with or without
00009   modification, are permitted provided that the following conditions
00010   are met:
00011   1. Redistributions of source code must retain the above copyright
00012      notice, this list of conditions and the following disclaimer.
00013   2. Redistributions in binary form must reproduce the above copyright
00014      notice, this list of conditions and the following disclaimer in
00015      the documentation and/or other materials provided with the
00016      distribution.
00017   3. The names of the authors may not be used to endorse or promote
00018      products derived from this software without specific prior
00019      written permission.
00020  
00021   THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS
00022   OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
00023   WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
00024   ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
00025   DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
00026   DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
00027   GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
00028   INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
00029   IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
00030   OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
00031   IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
00032 */
00033 
00034 
00035 
00036 #include <stdio.h>
00037 #include <errno.h>
00038 
00039 #include "zipint.h"
00040 
00041 
00042 
00043 
00044 int
00045 _zip_filerange_crc(FILE *fp, off_t start, off_t len, uLong *crcp,
00046                  struct zip_error *errp)
00047 {
00048     Bytef buf[BUFSIZE];
00049     size_t n;
00050 
00051     *crcp = crc32(0L, Z_NULL, 0);
00052 
00053     if (fseeko(fp, start, SEEK_SET) != 0) {
00054        _zip_error_set(errp, ZIP_ER_SEEK, errno);
00055        return -1;
00056     }
00057     
00058     while (len > 0) {
00059        n = len > BUFSIZE ? BUFSIZE : len;
00060        if ((n=fread(buf, 1, n, fp)) <= 0) {
00061            _zip_error_set(errp, ZIP_ER_READ, errno);
00062            return -1;
00063        }
00064 
00065        *crcp = crc32(*crcp, buf, n);
00066 
00067        len-= n;
00068     }
00069 
00070     return 0;
00071 }