On Feb 14, 2004, at 7:30 AM, Derk-Jan Hartman wrote:
For some strange reason our latest version of VLC OSX more than doubles the CPU usage of mad_frame_decode, specifically the imdct36 routine it would seem. It is an OS X problem only and very annoying. Decoding mp3 now requires 28% CPU usage on my G4/400 (used to be 12%).
libmad library version changes have been ruled out as the cause of this. Our mp3 decoder module didn't change either, but the demux module did change. We suspect it might be something like an alignment issue, but we can't seem to track it down..
Could you give some advice as to what might be the cause of this sudden increase in CPU usage, and how me may check some of our input for correctness?
I don't think alignment should be an issue since nothing in imdct36() depends on the alignment of the bitstream.
The only possibility I can see affecting the performance of imdct36() might be a possible change in compilation directives. The preprocessor symbols FPM_*, OPT_SPEED, and OPT_ACCURACY can all drastically affect performance, as can the selection of compiler optimization flags. You might check to make sure these have not changed.