[tremor] Ogg/Vorbis report, FFT optimizations

[timmy brolin]

>> Secondly, as far as I understand, when you compare the performance of 
>> the old MDCT with your new FFT based implementation, you are 
>> comparing:
>> A pure C implementation of a MDCT written specifically for processors 
>> with a 32*32bit multiplication instruction, but complied for a 
>> processor with only a 16*16bit multiplication instruction.
>> With:
>> A FFT based MDCT implementation where the FFT is highly asm optimised 
>> by Texas Instruments for this particular DSP.
>> Not a very fair comparison.
>
> That depends on your problem domain.  From his point of view, it 
> definitely _is_ a fair comparison.

That depends on what your are trying to show.
For a specific implementation, the comparison is valid. But if you
are trying to show that the FFT approch is faster than the original
MDCT code, then you should not compare optimized code against
unoptimized code.

>> The obvious fact that the original Tremor codebase is neither suited 
>> nor intended for 16bit processors shows clearly in table 7.4. 
>> According to that table, Tremor require 107MIPS to decode at 112kbps 
>> on your DSP. Tremor runs fine on a ~60MIPS ARM7.
>
> ...Which is pretty pathetic performance as well, really.

Yes, it is.
It would be great if it this FFT approch can improve this number.

>> I also spotted a small technical error on page 35.. It says the DSP 
>> requires all 16bit words to be aligned on 2-byte boundarys, all 32bit 
>> words on 4-byte boundarys, and that this is not the case on ARM 
>> processors..
>> Words must allways be properly aligned on all processors. This is not 
>> specific for your DSP.
>
> Words do *not* have to be aligned on al processors.

Ok, almost all.

/Timmy

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