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#include <stdio.h>
#include <grass/rowio.h>
static void *my_select(ROWIO *, int);
static void pageout(ROWIO *, int);
/*!
* \brief read a row
*
* Rowio_get() returns a
* buffer which holds the data for row <b>n</b> from the file associated with
* ROWIO structure <b>r.</b> If the row requested is not in memory, the
* <b>getrow()</b> routine specified in <i>rowio_setup</i> is called to
* read row <b>n</b> into memory and a pointer to the memory buffer containing
* the row is returned. If the data currently in the buffer had been changed by
* <i>rowio_put</i>, the <b>putrow()</b> routine specified in
* <i>rowio_setup</i> is called first to write the changed row to disk. If row
* <b>n</b> is already in memory, no disk read is done. The pointer to the data
* is simply returned.
* Return codes:
* NULL <b>n</b> is negative, or
* <b>getrow()</b> returned 0 (indicating an error condition).
* !NULL pointer to buffer containing row <b>n.</b>
*
* \param r
* \param n
* \return char *
*/
void *rowio_get(ROWIO * R, int row)
{
int i;
int age;
int cur;
if (row < 0)
return NULL;
if (row == R->cur)
return R->buf;
for (i = 0; i < R->nrows; i++)
if (row == R->rcb[i].row)
return my_select(R, i);
age = 0;
cur = 0;
for (i = 0; i < R->nrows; i++)
if (R->rcb[i].row < 0) { /* free slot ! */
cur = i;
break;
}
else if (age < R->rcb[i].age) {
cur = i;
age = R->rcb[i].age;
}
pageout(R, cur);
i = (*R->getrow) (R->fd, R->rcb[cur].buf, R->rcb[cur].row = row, R->len);
R->rcb[cur].dirty = 0;
if (!i) {
R->rcb[cur].row = -1;
if (cur == R->cur)
R->cur = -1;
return NULL;
}
return my_select(R, cur);
}
void rowio_flush(ROWIO * R)
{
int i;
for (i = 0; i < R->nrows; i++)
pageout(R, i);
}
static void pageout(ROWIO * R, int cur)
{
if (R->rcb[cur].row < 0)
return;
if (!R->rcb[cur].dirty)
return;
(*R->putrow) (R->fd, R->rcb[cur].buf, R->rcb[cur].row, R->len);
R->rcb[cur].dirty = 0;
}
static void *my_select(ROWIO * R, int n)
{
int i;
R->rcb[n].age = 0;
for (i = 0; i < R->nrows; i++)
R->rcb[i].age++;
R->cur = R->rcb[n].row;
R->buf = R->rcb[n].buf;
return R->buf;
}
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