AWARE [SYSTEMS]
AWare Systems, , Home TIFF and LibTiff Mailing List Archive

LibTiff Mailing List

TIFF and LibTiff Mailing List Archive
December 2018

Previous Thread
Next Thread

Previous by Thread
Next by Thread

Previous by Date
Next by Date

Contact

The TIFF Mailing List Homepage
Archive maintained by AWare Systems



New Datamatrix section



Valid HTML 4.01!



Thread

2018.12.11 13:36 "SeekOK and WriteOK", by Emmanuel Cosnard
2018.12.11 14:01 "Re: SeekOK and WriteOK", by Bob Friesenhahn
2018.12.11 14:09 "Re: SeekOK and WriteOK", by Emmanuel Cosnard
2018.12.11 14:24 "Re: SeekOK and WriteOK", by Emmanuel Cosnard
2018.12.11 14:29 "Re: SeekOK and WriteOK", by Nicolas Ruff
2018.12.11 18:54 "Re: SeekOK and WriteOK", by Bob Friesenhahn
2018.12.12 08:53 "Re: SeekOK and WriteOK", by Emmanuel Cosnard
2018.12.13 11:04 "Re: SeekOK and WriteOK", by Emmanuel Cosnard
2018.12.13 13:13 "Re: SeekOK and WriteOK", by Paavo Helde

2018.12.11 14:01 "Re: SeekOK and WriteOK", by Bob Friesenhahn

On Tue, 11 Dec 2018, Emmanuel Cosnard wrote:

> Hello,
>
> I am using the function TIFFWriteData to write some data on a custome
> rationnal tag, and it seems, that on some rare occasion,
> if (SeekOK(tif, dir->tdir_offset) && WriteOK(tif, cp, cc))
> Is there a way to do some intelligent retry here, instead of returning an
> error? Or can we know why the WriteOK or SeekOK didn't work properly?

You did not mention the operating system you are using or the size of 
its native off_t type (or equivalent).  It might make a difference if 
you are using tif_unix.c or tif_win32.c, and the capabilities of the 
compiler and run-time when the library was compiled.

This is the underlying implementation of the check:

int _TIFFSeekOK(TIFF* tif, toff_t off)
{
     /* Huge offsets, especially -1 / UINT64_MAX, can cause issues */
     /* See http://bugzilla.maptools.org/show_bug.cgi?id=2726 */
     return off <= (~(uint64)0)/2 && TIFFSeekFile(tif,off,SEEK_SET)==off;
}

One can see that the first check is that the offset must be within the 
range of a signed 64-bit type.  The next check actually does the seek 
and checks if the requested position was obtained.  This is a case 
where the seek position might need to be in the range of a smaller 
size.

Bob
-- 
Bob Friesenhahn
bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/
Public Key,     http://www.simplesystems.org/users/bfriesen/public-key.txt
_______________________________________________
Tiff mailing list
Tiff@lists.osgeo.org
https://lists.osgeo.org/mailman/listinfo/tiff