segment/init.c

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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
 * SPDX-FileCopyrightText: 2000-2009 GRASS Development Team
 * SPDX-License-Identifier: GPL-2.0-or-later
 *
 *****************************************************************************/
 
#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) == -1) {
        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;
}