[Libav-user] ff_log2_tab defined multiple times in the fmpeg 1.1 libraries, bug or feature ??

Hendrik Leppkes h.leppkes at gmail.com
Thu Feb 14 23:19:13 CET 2013

On Thu, Feb 14, 2013 at 10:53 PM, Lars Hammarstrand
<lars.hammarstrand at gmail.com> wrote:
> Hello folks!
> I found the original patch: avutil: Duplicate ff_log2_tab instead of sharing
> it across libs.
> The objectives for this patch was: "The table is so small that the space
> gain is not worth the performance overhead of cross-library access" (:uhu:).
> I have never heard of such a thing as "cross-library access" that
> "auto-magic" gives you a performance gain when you allocate the exact same
> object file to different link libraries in the same distribution package.
> Looking forward to have this "unpatched" ...

Please don't top post on this mailing list.

In any case, this patch was focused on shared library builds, and
importing data symbols from shared libraries does add an extra level
of indirection.
However, not only that, it would also require exporting a ff* private
symbol from avutil, and adds a lot of complexity when dealing with
shared library builds on some systems (eg. MSVC)

It may not do anything for static builds, but it also didn't cause any
issues in sane build environments (all the ffmpeg applications still
build fine for example), so it may as well be a problem on your end.

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