Date: Sun, 18 Feb 1996 15:07:43 +0200 (IST)
From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
To: Robert Hoehne <rho AT hrz DOT tu-chemnitz DOT de>
Cc: djgpp AT delorie DOT com, DJ Delorie <dj AT delorie DOT com>
Subject: Re: Patch 2.1 from DJGPP V2.0 doesn't work
In-Reply-To: <4fv73i$dhn@pyrrhus-f.hrz.tu-chemnitz.de>
Message-Id: <Pine.SUN.3.91.960218145130.29485A-100000@is>
Mime-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII


On 15 Feb 1996, Robert Hoehne wrote:

> Patch 2.1 from DJGPP V2.0 doesn't work
[snipp]
>   Hmm...  Looks like a new-style context diff to me...
>   Exiting due to signal SIGABRT
>   Assertion failed at pch.c line 409: p_base <= file_pos
> 
> 
> I think, this is only an error in compiling patch.

No, it's a bug in the library function `ftell' (unless I didn't understand
its code).  It incorrectly assumes that, for files open for reading, the
position returned by `lseek (file, 0L, SEEK_CUR)' corresponds to the
*beginning* of the buffered portion of the file.  The truth is, that it
corresponds to the *end* of that buffered portion.  Below please find a
patch to fix this problem.  When linked with the fixed version of `ftell',
`patch' works under v2.0 (at least for the simple test submitted by
Robert).  The test program `fseek' from djtst200.zip also succeeds with
the fixed version of `ftell', except with Unix-style text files (without a
CR before each NL) in TEXT mode.  The original code also failed in that
case, and IMHO there is no way to make it work unless some low-level
library function (like `filbuf') detects that this is a Unix-style file
and sets a flag which could be tested by `ftell'.  DJ, can we make such a
change?  I can submit it, if we decide to do it (but then I already
submitted it once and it wasn't installed ;-). 

*** ansi/stdio/ftell.c~0	Mon Feb  5 00:13:42 1996
--- ansi/stdio/ftell.c	Sun Feb 18 14:35:22 1996
***************
*** 17,44 ****
      f->_cnt = 0;
    if (f->_flag&_IOREAD)
    {
      if (__file_handle_modes[f->_file] & O_TEXT) /* if a text file */
      {
!       if (f->_cnt && f->_ptr != f->_base)
        {
  	char *cp;
! 	adjust = - f->_bufsiz + (f->_ptr-f->_base);
! 	for (cp=f->_base; cp < f->_ptr; cp++) /* for every char in buf */
! 	  if (*cp == '\n')	/* if it's LF */
! 	    adjust++;		/* there was a CR also */
        }
      }
-     else
-       adjust = - f->_cnt;
    }
    else if (f->_flag&(_IOWRT|_IORW))
    {
!     adjust = 0;
      if (f->_flag&_IOWRT && f->_base && (f->_flag&_IONBF)==0)
      {
!       adjust = f->_ptr - f->_base;
        if (__file_handle_modes[f->_file] & O_TEXT)
! 	for (idx=0; idx<adjust; idx++)
  	  if (f->_base[idx] == '\n')
  	    adjust++;
      }
--- 17,55 ----
      f->_cnt = 0;
    if (f->_flag&_IOREAD)
    {
+     /* When reading files, the file position known by `lseek' is
+      at the end of the buffered portion of the file.  So `adjust'
+      is negative (current buf position is BEFORE the one returned
+      by `lseek') and, for TEXT files, it gets decremented (larger
+      in absolute value) for every NL from current pos to the end
+      of the buffer, to account for stripped CR characters.  */
+     adjust = - f->_cnt;
+ 
      if (__file_handle_modes[f->_file] & O_TEXT) /* if a text file */
      {
!       if (f->_cnt)
        {
  	char *cp;
! 
!         /* For every char in buf AFTER current pos... */
! 	for (cp=f->_ptr + f->_cnt - 1; cp >= f->_ptr; cp--)
! 	  if (*cp == '\n')	/* ...if it's LF... */
! 	    adjust--;		/* ...there was a CR also */
        }
      }
    }
    else if (f->_flag&(_IOWRT|_IORW))
    {
!     /* When writing a file, the current file position known by `lseek'
!        is at the beginning of the buffered portion of the file.  We
!        have to adjust it by our offset from the beginning of the buffer,
!        and account for the CR characters which will be added by `write'.  */
      if (f->_flag&_IOWRT && f->_base && (f->_flag&_IONBF)==0)
      {
!       int lastidx = adjust = f->_ptr - f->_base;
! 
        if (__file_handle_modes[f->_file] & O_TEXT)
! 	for (idx=0; idx < lastidx; idx++)
  	  if (f->_base[idx] == '\n')
  	    adjust++;
      }