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/****************************************************************************
*
* MODULE: segment
* AUTHOR(S): CERL
* Bernhard Reiter <bernhard intevation.de>,
* Brad Douglas <rez touchofmadness.com>,
* Glynn Clements <glynn gclements.plus.com>,
* Markus Neteler <neteler itc.it>,
* Markus Metz <markus.metz.giswork googlemail.com>
* PURPOSE: Segment initialization routines
* COPYRIGHT: (C) 2000-2009 by the GRASS Development Team
*
* This program is free software under the GNU General Public
* License (>=v2). Read the file COPYING that comes with GRASS
* for details.
*
*****************************************************************************/
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <grass/gis.h>
#include "local_proto.h"
static int read_int(int, int *);
static int read_off_t(int, off_t *);
/* fd must be open for read and write */
/**
* \fn int Segment_init (SEGMENT *SEG, int fd, int nseg)
*
* \brief Initialize segment structure.
*
* Initializes the <b>seg</b> structure. The file on <b>fd</b> is
* a segment file created by <i>Segment_format()</i> and must be open
* for reading and writing. The segment file configuration parameters
* <i>nrows, ncols, srows, scols</i>, and <i>len</i>, as written to the
* file by <i>Segment_format()</i>, are read from the file and stored in
* the <b>seg</b> structure. <b>nsegs</b> specifies the number of
* segments that will be retained in memory. The minimum value allowed
* is 1.
*
* <b>Note:</b> The size of a segment is <em>scols*srows*len</em> plus a
* few bytes for managing each segment.
*
* \param[in,out] SEG segment
* \param[in] fd file descriptor
* \param[in] nseg number of segments to remain in memory
* \return 1 if successful
* \return -1 if unable to seek or read segment file
* \return -2 if out of memory
*/
int Segment_init(SEGMENT *SEG, int fd, int nseg)
{
SEG->open = 0;
SEG->fd = fd;
SEG->nseg = nseg;
if (lseek(fd, 0L, SEEK_SET) < 0) {
int err = errno;
G_warning("Segment_init: %s", strerror(err));
return -1;
}
/* read the header */
if (!read_off_t(fd, &SEG->nrows) || !read_off_t(fd, &SEG->ncols) ||
!read_int(fd, &SEG->srows) || !read_int(fd, &SEG->scols) ||
!read_int(fd, &SEG->len))
return -1;
return seg_setup(SEG);
}
static int read_int(int fd, int *n)
{
int bytes_read;
if ((bytes_read = read(fd, n, sizeof(int))) == -1)
G_warning("read_int: %s", strerror(errno));
bytes_read = (bytes_read == sizeof(int));
return bytes_read;
}
static int read_off_t(int fd, off_t *n)
{
int bytes_read;
if ((bytes_read = read(fd, n, sizeof(off_t))) == -1)
G_warning("read_off_t: %s", strerror(errno));
bytes_read = (bytes_read == sizeof(off_t));
return bytes_read;
}
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