Re: imdct36 CPU usage increase

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.

-- 
Rob Leslie
[email protected]