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Date: Sun, 19 Nov 2006 15:20:39 -0600 (CST)
From: Bob Friesenhahn <bfriesen@simple.dallas.tx.us>
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To: Paul Surgeon <surgpm@cybersmart.co.za>
Subject: Re: [Tiff] tiffinfo large file issue
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On Sun, 19 Nov 2006, Paul Surgeon wrote:

> On Sunday 19 November 2006 23:12, Frank Warmerdam wrote:
>> Paul,
>>
>> My guess would be that it works on files where the directory data is
>> before the 2GB mark.
>
> Hmmm ... I'm not sure what you mean.
> Care to elaborate?

The tiffinfo utility primarily reads TIFF directories, which may occur 
almost anywhere in the file.  If the TIFF directory is placed at the 
end of a file which is over 2GB in size, then a file offet value 
bigger than 2GB is necessary to retrieve it.  Systems which do not 
support large files often use a signed 32-bit integer value to 
represent file offsets (off_t type), and this value overflows at the 
2GB offset.  Some systems (e.g. Linux and Solaris) require special 
compilation options in order to use larger file offsets (signed 64-bit 
integer) in programs so that the programs can support large files.

If all the offsets necessary to access the TIFF directories are less 
than 2GB, then it may be possible to usefully access the file even if 
the image raster data causes the file to be larger than 2GB.

Bob
======================================
Bob Friesenhahn
bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/

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