Re: Multi Channel FFT Audio Anaylzer + Question
Re: Multi Channel FFT Audio Anaylzer + Question
- Subject: Re: Multi Channel FFT Audio Anaylzer + Question
- From: Frank Schoep <email@hidden>
- Date: Wed, 27 Jun 2007 11:59:24 +0200
On Jun 27, 2007, at 12:38 AM, Benjamin Federer wrote:
… The vDSP library shows some sample code that uses the
"vec_malloc" statement. Unfortunately I could not get Xcode to like
it. Instead I had to use "malloc". Frank Schoep's homepage states
the use of a "__attribute__ ((aligned))" postfix for GCC. I could
not manage to find any specific information about vector alignment
in the vDSP documentation. Any clues?
Hello Benjamin,
Being a mere mortal I explored the Accelerate framework on my own
with the API guides besides me. In almost every function description
there is an explanation as to what scenario invokes scalar code and
what conditions are required for vectorized code.
It just so happens that the "Automatically align variables" or
something aptly named like that in Xcode doesn't work for vDSP calls
and variables so I saw quite abysmal performance. In my case, just
appending the postfix helped invoke vectorized code on at least Intel
Core Duo.
I think you're be able to use "Shark" from the CHUD package to see
whether or not vectorized code is invoked. At least, I used Shark to
check this myself. Look for function naming differences between
scalar and vectorized when profiling.
I hope that was moderately useful.
Sincerely,
Frank
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