RE: OldStylePdfWriter writes wrong /Size in trailer, XRef doesn't count objects correctly

[Jozef M. <mis...@ho...>]

hey gwurk, 
thx a lot. 

michal will be here in 2 weeks time. i put it into bugtracker that we do not forget it

jozo

> Date: Wed, 30 Apr 2008 19:30:49 -0400
> From: gw...@fi...
> To: pdf...@li...
> Subject: OldStylePdfWriter writes wrong /Size in trailer,	XRef doesn't count objects correctly
> 
> Hi again,
> 
> I noticed a problem where PDFedit seems to write an incorrect /Size
> entry in the new trailer it adds. Suppose the PDF we're editing has 5
> entries in its xref table, but only 2 are used:
> 
> xref
> 0 5
> 0000000001 65535 f
> 0000000002 00001 f
> 0000000000 00001 f
> 0000000123 00000 n
> 0000000456 00000 n
> trailer << /Size 5  /Root 4 0 R >>
> 
> In OldStylePdfWriter::writeTrailer(), we compute the new /Size as:
>     std::max(prevSection.objNum, (size_t)(maxObjNum + 1))
> 
> and prevSection.objNum is set by the caller XRefWriter::saveChanges():
>     secInfo={lastXRefPos, XRef::getNumObjects()};
> 
> And looking at XRef::getNumObjects(), it's defined as:
>     virtual int getNumObjects()
>     {
>        int count=0;
>        for(int i=0; i<size; i++)
>           // counts just not free entries
>           if(entries[i].type != xrefEntryFree)
>              count++;
> 
>        return count;
>     }
> 
> Notice that it just counts the number of used entries; it does not
> return the number of the LAST used entry. So XRef::getNumObjects()
> would return 2, even though the xref table had 5 entries. If we wrote
> a new trailer with this information, it would have the wrong /Size.
> 
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