[tremor] Re: [vorbis-dev] Optimizing Vorbis for a DSP

Johannes Sandvall js at sandvall.nu
Mon Mar 29 12:17:39 PST 2004

On Sun 28 Mar 2004 23:23:46 CEST, Graham Mitchell wrote:
> > I have recently ported Vorbis to a Texas instruments DSP (TMS320C5510),
> > The problem I have is that it is not decoding the audio in real time(
> > about 50% of real time). Could any one give me a clue in which area I
> > could start to optimize the code.
> Well, a few weeks ago Johannes Sandvall posted to the list about "replacing 
> the IMDCT with a N/4 FFT", which I seem to recall gave a large speedup; his 
> report is here:
> 	http://www.sandvall.nu/thesis.pdf
> And my crufty brain seems to recall that profiling has determined that more 
> time is spent in the function "mdct_backward" than any other, but I could be 
> way off base.
> Others on the list are much more qualified than I am, but sometimes a faster, 
> mediocre response is better than a slower, perfect one.  At least that's 
> what I'm banking on, anyway.

Here is maybe a patch of the code. Should include both optimized TI
assembler and reference c code. Patch available at:

It's for the lowmem branch of Tremor. One of the ways to install the
patch is:

dir_of_tremor_checkout$ cat patch | patch -p1

/ Johannes Sandvall
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