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/**
* \file lib/segment/get_row.c
*
* \brief Segment row retrieval routines.
*
* This program is free software under the GNU General Public License
* (>=v2). Read the file COPYING that comes with GRASS for details.
*
* \author GRASS GIS Development Team
*
* \date 2005-2018
*/
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <grass/gis.h>
#include "local_proto.h"
/**
* \fn int Segment_get_row (SEGMENT *SEG, void *buf, int row)
*
* \brief Read row from segment file.
*
* Transfers data from a segment file, row by row, into memory
* (which can then be written to a regular matrix file). <b>Seg</b> is the
* segment structure that was configured from a call to
* <i>Segment_init()</i>.
*
* <b>Buf</b> will be filled with <em>ncols*len</em> bytes of data
* corresponding to the <b>row</b> in the data matrix.
*
* \param[in] seg segment
* \param[in,out] buf
* \param[in] row
* \return 1 if successful
* \return -1 if unable to seek or read segment file
*/
int Segment_get_row(const SEGMENT *SEG, void *buf, off_t row)
{
int size;
off_t ncols, col;
int scols;
int n, index;
if (SEG->cache) {
memcpy(buf, SEG->cache + ((size_t)row * SEG->ncols) * SEG->len,
SEG->len * SEG->ncols);
return 1;
}
ncols = SEG->ncols - SEG->spill;
scols = SEG->scols;
size = scols * SEG->len;
for (col = 0; col < ncols; col += scols) {
SEG->address(SEG, row, col, &n, &index);
SEG->seek(SEG, n, index);
if (read(SEG->fd, buf, size) != size) {
G_warning("Segment_get_row: %s", strerror(errno));
return -1;
}
/* The buf variable is a void pointer and thus points to anything. */
/* Therefore, it's size is unknown and thus, it cannot be used for */
/* pointer arithmetic (some compilers treat this as an error - SGI */
/* MIPSPro compiler for one). Since the read command is reading in */
/* "size" bytes, cast the buf variable to char * before incrementing */
buf = ((char *)buf) + size;
}
if ((size = SEG->spill * SEG->len)) {
SEG->address(SEG, row, col, &n, &index);
SEG->seek(SEG, n, index);
if (read(SEG->fd, buf, size) != size) {
G_warning("Segment_get_row: %s", strerror(errno));
return -1;
}
}
return 1;
}
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