[Bug 772864] New: audioconvert: mask calculation optimization

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=772864

            Bug ID: 772864
           Summary: audioconvert: mask calculation optimization
    Classification: Platform
           Product: GStreamer
           Version: 1.8.3
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: Normal
         Component: gst-plugins-base
          Assignee: gstreamer-bugs at lists.freedesktop.org
          Reporter: brain at jikos.cz
        QA Contact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---

The n_bits_set() function in gstaudioconvert.c, i.e. the "popcount", uses the
worst algorithm available, with complexity of O(n).

There are better algorithms available, see:
https://en.wikipedia.org/wiki/Hamming_weight
I'd opt for the popcount_3 or popcount_4 algorithms mentioned at Wikipedia.

GCC also has the __builtin_popcountl() function, which translates to a CPU
instruction if the underlying hardware supports it.

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