| /* 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. |
| |
| In addition to the permissions in the GNU General Public License, the |
| Free Software Foundation gives you unlimited permission to link the |
| compiled version of this file into combinations with other programs, |
| and to distribute those combinations without any restriction coming |
| from the use of this file. (The General Public License restrictions |
| do apply in other respects; for example, they cover modification of |
| the file, and distribution when not linked into a combine |
| executable.) |
| |
| 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 <string.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 m, new; |
| int length; |
| char *p; |
| |
| length = sizeof (gfc_offset); |
| |
| p = salloc_r_at (current_unit->s, &length, |
| file_position (current_unit->s) - length); |
| if (p == NULL) |
| goto io_error; |
| |
| memcpy (&m, p, sizeof (gfc_offset)); |
| new = file_position (current_unit->s) - m - 2*length; |
| if (sseek (current_unit->s, new) == FAILURE) |
| goto io_error; |
| |
| current_unit->last_record--; |
| return; |
| |
| io_error: |
| generate_error (ERROR_OS, NULL); |
| } |
| |
| |
| extern void st_backspace (void); |
| export_proto(st_backspace); |
| |
| 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 (file_position (u->s) == 0) |
| goto done; /* Common special case */ |
| |
| if (u->mode == WRITING) |
| { |
| flush (u->s); |
| struncate (u->s); |
| u->mode = READING; |
| } |
| |
| if (u->flags.form == FORM_FORMATTED) |
| formatted_backspace (); |
| else |
| unformatted_backspace (); |
| |
| u->endfile = NO_ENDFILE; |
| u->current_record = 0; |
| } |
| |
| done: |
| library_end (); |
| } |