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September 2004
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2004.09.17 04:20 "Re: BigTIFF Tag Value Count issue", by Bob Friesenhahn
On Thu, 16 Sep 2004, Chris Cox wrote: > > > Option 0: stick with 4 byte tag count members (alignment, tag data <= 4 > > > gig, Frank's choice) > > > Option 1: make it an 8 byte tag count (no alignment, tag data > 4 gig > > > allowed) > > > Option 2, courtesy of Bob: make it 8 byte tag count, add 4 padding bytes > > > (alignment, tag data > 4 gig allowed) > > > > > > Can I put you down as an option 2 vote, or were you merely signalling > > > the option? > > > > Sure, there should always be a second option so put me down for option 2. > > :-) > > Can you think of a situation that needs an 8 byte count? > Or do you just want the size increased on general principles? The idea was to consume 8 bytes for alignment purposes but use 4 bytes out of those 8 bytes to support the value. Perhaps I misunderstood the problem. I don't have a strong opinion either way, but do believe that the format should be aligned to work well with memory-mapping. If someone wants to create a tiff-bomb, they can do it just as easily with 4GB as they can with 1TB. In fact, the 4GB attack is more likely to cause a problem since the machine is more likely to perform the request. > Do you think that increasing the count to 8 bytes would be a problem in > libTIFF? I don't have the libtiff knowledge to properly answer that. If the availability of a native 64-bit storage type can be assumed (pretty safe if 32-bit processors are the new baseline) then it doesn't sound like an 8 byte value would be a problem. Bob ====================================== Bob Friesenhahn bfriesen@simple.dallas.tx.us http://www.simplesystems.org/users/bfriesen