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List:       zlib-devel
Subject:    [Zlib-devel] zlib 1.2.3.1 released for testing
From:       madler () alumni ! caltech ! edu (Mark Adler)
Date:       2006-09-20 4:54:13
Message-ID: E1543049-9D7F-4AA1-9E41-D0CEC6817F0E () alumni ! caltech ! edu
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On Sep 19, 2006, at 7:31 PM, Cosmin Truta wrote:
> I don't think I like the idea of hurting zlib users who want the
> inflation as fast as possible, for the sake of sloppy web designers.

The modification I came up with does not slow down inflate.  All of  
the extra code is inside the if-statements that previously returned  
the error condition.  So no additional code is executed unless an  
invalid distance too far is detected.

Dictionaries can in fact be set for raw inflate.  However your  
solution would require setting a 32K dictionary for every PNG image  
decompression.  Unfortunately, you don't know beforehand if the PNG  
image is one of the invalid ones.  That requires copying 32K bytes  
every time.  That would unnecessarily slow down the application in  
question, which is a web browser that desperately wants to have  
exactly the same buggy behavior as Internet Explorer.  The  
implemented solution only comes into play if and when the deflate  
stream is discovered to be invalid.

mark




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