1 /*
2 zip_filerange_crc.c -- compute CRC32 for a range of a file
3 Copyright (C) 2008 Dieter Baron and Thomas Klausner
4
5 This file is part of libzip, a library to manipulate ZIP archives.
6 The authors can be contacted at <libzip@nih.at>
7
8 Redistribution and use in source and binary forms, with or without
9 modification, are permitted provided that the following conditions
10 are met:
11 1. Redistributions of source code must retain the above copyright
12 notice, this list of conditions and the following disclaimer.
13 2. Redistributions in binary form must reproduce the above copyright
14 notice, this list of conditions and the following disclaimer in
15 the documentation and/or other materials provided with the
16 distribution.
17 3. The names of the authors may not be used to endorse or promote
18 products derived from this software without specific prior
19 written permission.
20
21 THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS
22 OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
23 WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
25 DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
27 GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
28 INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
29 IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
30 OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
31 IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
32 */
33
34
35
36 #include <stdio.h>
37 #include <errno.h>
38
39 #include "zipint.h"
40
41
42
43
44 int
_zip_filerange_crc(FILE * fp,off_t start,off_t len,uLong * crcp,struct zip_error * errp)45 _zip_filerange_crc(FILE *fp, off_t start, off_t len, uLong *crcp,
46 struct zip_error *errp)
47 {
48 Bytef buf[BUFSIZE];
49 size_t n;
50
51 *crcp = crc32(0L, Z_NULL, 0);
52
53 if (fseeko(fp, start, SEEK_SET) != 0) {
54 _zip_error_set(errp, ZIP_ER_SEEK, errno);
55 return -1;
56 }
57
58 while (len > 0) {
59 n = len > BUFSIZE ? BUFSIZE : len;
60 if ((n=fread(buf, 1, n, fp)) <= 0) {
61 _zip_error_set(errp, ZIP_ER_READ, errno);
62 return -1;
63 }
64
65 *crcp = crc32(*crcp, buf, n);
66
67 len-= n;
68 }
69
70 return 0;
71 }
72
