mirror of git://gcc.gnu.org/git/gcc.git
162 lines
3.7 KiB
C
162 lines
3.7 KiB
C
/* Copyright (C) 2002-2003 Free Software Foundation, Inc.
|
|
Contributed by Andy Vaught
|
|
|
|
This file is part of the GNU Fortran 95 runtime library (libgfortran).
|
|
|
|
Libgfortran is free software; you can redistribute it and/or modify
|
|
it under the terms of the GNU General Public License as published by
|
|
the Free Software Foundation; either version 2, or (at your option)
|
|
any later version.
|
|
|
|
Libgfortran is distributed in the hope that it will be useful,
|
|
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
GNU General Public License for more details.
|
|
|
|
You should have received a copy of the GNU General Public License
|
|
along with Libgfortran; see the file COPYING. If not, write to
|
|
the Free Software Foundation, 59 Temple Place - Suite 330,
|
|
Boston, MA 02111-1307, USA. */
|
|
|
|
#include "config.h"
|
|
#include "libgfortran.h"
|
|
#include "io.h"
|
|
|
|
/* backspace.c -- Implement the BACKSPACE statement */
|
|
|
|
/* formatted_backspace(void)-- Move the file back one line. The
|
|
* current position is after the newline that terminates the previous
|
|
* record, and we have to sift backwards to find the newline before
|
|
* that or the start of the file, whichever comes first. */
|
|
|
|
#define READ_CHUNK 4096
|
|
|
|
static void
|
|
formatted_backspace (void)
|
|
{
|
|
gfc_offset base;
|
|
char *p;
|
|
int n;
|
|
|
|
base = file_position (current_unit->s) - 1;
|
|
|
|
do
|
|
{
|
|
n = (base < READ_CHUNK) ? base : READ_CHUNK;
|
|
base -= n;
|
|
|
|
p = salloc_r_at (current_unit->s, &n, base);
|
|
if (p == NULL)
|
|
goto io_error;
|
|
|
|
/* Because we've moved backwords from the current position, it
|
|
* should not be possible to get a short read. Because it isn't
|
|
* clear what to do about such thing, we ignore the possibility. */
|
|
|
|
/* There is no memrchr() in the C library, so we have to do it
|
|
* ourselves. */
|
|
|
|
n--;
|
|
while (n >= 0)
|
|
{
|
|
if (p[n] == '\n')
|
|
{
|
|
base += n + 1;
|
|
goto done;
|
|
}
|
|
|
|
n--;
|
|
}
|
|
|
|
}
|
|
while (base != 0);
|
|
|
|
/* base is the new pointer. Seek to it exactly */
|
|
|
|
done:
|
|
if (sseek (current_unit->s, base) == FAILURE)
|
|
goto io_error;
|
|
current_unit->last_record--;
|
|
current_unit->endfile = NO_ENDFILE;
|
|
|
|
return;
|
|
|
|
io_error:
|
|
generate_error (ERROR_OS, NULL);
|
|
}
|
|
|
|
|
|
/* unformatted_backspace()-- Move the file backwards for an
|
|
* unformatted sequential file. We are guaranteed to be between
|
|
* records on entry and we have to shift to the previous record. */
|
|
|
|
static void
|
|
unformatted_backspace (void)
|
|
{
|
|
gfc_offset *p, new;
|
|
int length;
|
|
|
|
length = sizeof (gfc_offset);
|
|
|
|
p = (gfc_offset *) salloc_r_at (current_unit->s, &length,
|
|
file_position (current_unit->s) - length);
|
|
if (p == NULL)
|
|
goto io_error;
|
|
|
|
new = file_position (current_unit->s) - *p - length;
|
|
if (sseek (current_unit->s, new) == FAILURE)
|
|
goto io_error;
|
|
|
|
current_unit->last_record--;
|
|
return;
|
|
|
|
io_error:
|
|
generate_error (ERROR_OS, NULL);
|
|
}
|
|
|
|
|
|
void
|
|
st_backspace (void)
|
|
{
|
|
gfc_unit *u;
|
|
|
|
library_start ();
|
|
|
|
u = find_unit (ioparm.unit);
|
|
if (u == NULL)
|
|
{
|
|
generate_error (ERROR_BAD_UNIT, NULL);
|
|
goto done;
|
|
}
|
|
|
|
current_unit = u;
|
|
|
|
/* Ignore direct access. Non-advancing I/O is only allowed for
|
|
* formatted sequential I/O and the next direct access transfer
|
|
* repositions the file anyway. */
|
|
|
|
if (u->flags.access == ACCESS_DIRECT)
|
|
goto done;
|
|
|
|
/* Check for special cases involving the ENDFILE record first */
|
|
|
|
if (u->endfile == AFTER_ENDFILE)
|
|
u->endfile = AT_ENDFILE;
|
|
else
|
|
{
|
|
if (u->current_record)
|
|
next_record (1);
|
|
|
|
if (file_position (u->s) == 0)
|
|
goto done; /* Common special case */
|
|
|
|
if (u->flags.form == FORM_FORMATTED)
|
|
formatted_backspace ();
|
|
else
|
|
unformatted_backspace ();
|
|
}
|
|
|
|
done:
|
|
library_end ();
|
|
}
|