[gstreamer-bugs] [Bug 533075] New: gst_rtp_buffer_compare_seqnum doesn't do what it says

[GStreamer (bugzilla.gnome.org)]

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  GStreamer | gst-plugins-base | Ver: HEAD CVS
           Summary: gst_rtp_buffer_compare_seqnum doesn't do what it says
           Product: GStreamer
           Version: HEAD CVS
          Platform: Other
        OS/Version: All
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: gst-plugins-base
        AssignedTo: gstreamer-bugs at lists.sourceforge.net
        ReportedBy: b-gnome at largestprime.net
         QAContact: gstreamer-bugs at lists.sourceforge.net
     GNOME version: Unspecified
   GNOME milestone: Unspecified


A recent comment change for gst_rtp_buffer_compare_seqnum says that it will
return the difference in sequence numbers. In its current implementation, it
does not. e.g. gst_rtp_buffer_compare_seqnum(0xFFFF, 0) returns 65535, not -1
as desired.

A much easier approach is to cast the difference into a signed gint16, then
into an gint (the function's return type), then the compiler and OS takes care
of the wraparound and sign extension for you. e.g.

gint
gst_rtp_buffer_compare_seqnum (guint16 seqnum1, guint16 seqnum2)
{
  return (gint16)(seqnum2-seqnum1);
}

This survives this simple test below (apologies for not making it an
attachment), where as the original function (revision 1.22 of gstrtpbuffer.c)
does not.

void test()
{
  int i, diff;
  uint16 a, b;
  for (diff = -100; diff < 100; diff++) {
    a = 0;
    for (i = 0; i < 0x20000; i++) {
      b = a + diff;
      assert(gst_rtp_buffer_compare_seqnum(a, b) == diff);
      a++;
    }
  }
}


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