GRASS GIS 8 Programmer's Manual 8.2.0(2022)-exported
segment/seek.c
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1
2/**
3 * \file lib/segment/seek.c
4 *
5 * \brief Segment seek routines.
6 *
7 * This program is free software under the GNU General Public License
8 * (>=v2). Read the file COPYING that comes with GRASS for details.
9 *
10 * \author GRASS GIS Development Team
11 *
12 * \date 2005-2009
13 */
14
15#include <stdio.h>
16#include <sys/types.h>
17#include <unistd.h>
18#include <string.h>
19#include <errno.h>
20#include <grass/gis.h>
21#include "local_proto.h"
22
23
24/**
25 * \brief Internal use only
26 *
27 * Seek into a segment.
28 *
29 * \param[in,out] SEG segment
30 * \param[in] n
31 * \param[in] index
32 * \return 0 on success
33 * \return -1 if unable to seek
34 */
35
36#define SEG_SEEK_FAST(SEG, n, index) \
37 ((((off_t) (n)) << (SEG)->sizebits) + (index) + (SEG)->offset)
38
39#define SEG_SEEK_SLOW(SEG, n, index) \
40 ((off_t) (n) * (SEG)->size + (index) + (SEG)->offset)
41
42int seg_seek_fast(const SEGMENT * SEG, int n, int index)
43{
44 if (lseek((SEG)->fd, SEG_SEEK_FAST(SEG, n, index),
45 SEEK_SET) == (off_t) -1) {
46 G_fatal_error("Segment seek: %s", strerror(errno));
47 }
48
49 return 0;
50}
51
52int seg_seek_slow(const SEGMENT * SEG, int n, int index)
53{
54 if (lseek((SEG)->fd, SEG_SEEK_SLOW(SEG, n, index),
55 SEEK_SET) == (off_t) -1) {
56 G_fatal_error("Segment seek: %s", strerror(errno));
57 }
58
59 return 0;
60}
61
62int seg_seek(const SEGMENT * SEG, int n, int index)
63{
64 return SEG->seek(SEG, n, index);
65}
void G_fatal_error(const char *msg,...)
Print a fatal error message to stderr.
Definition: gis/error.c:160
int seg_seek(const SEGMENT *SEG, int n, int index)
Definition: segment/seek.c:62
int seg_seek_fast(const SEGMENT *SEG, int n, int index)
Definition: segment/seek.c:42
int seg_seek_slow(const SEGMENT *SEG, int n, int index)
Definition: segment/seek.c:52
#define SEG_SEEK_FAST(SEG, n, index)
Internal use only.
Definition: segment/seek.c:36
#define SEG_SEEK_SLOW(SEG, n, index)
Definition: segment/seek.c:39