[Bug 731442] New: bytereader: optimize _scan_for_start_code() using pointer access

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=731442
  GStreamer | gstreamer (core) | git

           Summary: bytereader: optimize _scan_for_start_code() using
                    pointer access
    Classification: Platform
           Product: GStreamer
           Version: git
        OS/Version: All
            Status: UNCONFIRMED
          Keywords: perf
          Severity: enhancement
          Priority: Normal
         Component: gstreamer (core)
        AssignedTo: gstreamer-bugs at lists.freedesktop.org
        ReportedBy: baver.bae at lge.com
         QAContact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: Unversioned Enhancement


Created an attachment (id=278185)
 View: https://bugzilla.gnome.org/attachment.cgi?id=278185
 Review: https://bugzilla.gnome.org/review?bug=731442&attachment=278185

001_gstbytereader_improved_by_pointer_access.patch

This is a sub thread of the following:
https://bugzilla.gnome.org/show_bug.cgi?id=730783

Currently the scan uses Boyer-moore method and its performance is good.
but, it can be optimized from an implementation of view.

The original scan code is implemented by byte array and index-based access.
In _scan_for_start_code(), the index is increasing from start to end and the
base address of the byte array is referred to as return value.

In the case, index-based access can be replaced by pointer access, which
improve the performance by removing index-related operations.

Its performace is enhanced by approximately 8% on arm-based embedded devices.
Although it seems trivial, it can affect the overall performance because the
_scan_for_start_code() function is very often called when H.264/H.265 video is
played.

In addition, the technique can apply for all architectures and it is good in
view of readability and maintainability.

I attached a patch file.

If you have a problem or question, let me know it.
After reviewing this, please apply it to git repository.

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