All,
The below question came up in the context of a LibreOffice unit test,
where LibreOffice writes out a PNG image (involving zlib for
compression) and the test checked the exact sequence of bytes, which
failed on aarch64 when using Fedora's zlib. (Though the resulting
images look rather identical. Full thread starting at
<https://lists.freedesktop.org/archives/libreoffice/2020-August/085792.html>
"CppunitTest_sw_htmlexport failing due to zlib variation?")
Given the Fedora zlib aarch64 optimization patches quoted below: Does
anybody know whether it is indeed the case that the above scenario
(client code using zlib to generate a PNG image) can legitimately
generate varying output depending on zlib implementation details? Or
would that rather indicate a bug somewhere?
Thanks,
Stephan
-------- Forwarded Message --------
Subject: Re: CppunitTest_sw_htmlexport failing due to zlib variation?
Date: Wed, 26 Aug 2020 08:37:15 +0200
From: Stephan Bergmann <sbergman@xxxxxxxxxx>
To: libreoffice@xxxxxxxxxxxxxxxxxxxxx
On 25/08/2020 11:07, Stephan Bergmann wrote:
At least when building recent master on recent Fedora rawhide aarch64
with (among others) --with-system-zlib, CppunitTest_sw_htmlexport fails
with
[...]
The base64-encoded payload apparently is a PNG image. And from what
little I know about PNG, it looks plausible to me that there can be
different (compressed) PNG content that decompress to identical raw
data, and that the LibreOffice code would be allowed to generate
differing (compressed) PNG content for the above data:image/png URL
payload.
What supports the theory that "the LibreOffice code would be allowed to
generate differing (compressed) PNG content" is the Fedora zlib commit
<https://src.fedoraproject.org/rpms/zlib/c/25e9802713484882c27c1f979a6610a42414ee13>
"aarch64 optimizations", adding lots of code that presumably is only
relevant for aarch64 and presumably changes details of the compression
algorithm.
_______________________________________________
devel mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxx
To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxx
Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/
List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines
List Archives: https://lists.fedoraproject.org/archives/list/devel@xxxxxxxxxxxxxxxxxxxxxxx
