Thanks Takehiro.
(1) Could you also please provide an overview of and clarify the parameters
to fft_long() ?
void fft_long(lame_internal_flags * const gfc,
FLOAT x[BLKSIZE], int chn, const sample_t *buffer[2] )
- gfc is used to obtain a pointer to the blackman window, of size ???
- x contains the data to be transformed, in sequential order ???
- chn = ???
- buffer = ??? sample data, left/right channel???
(2) Apple's vDSP library features an "In-Place Real Fourier Transform".
Hence, I'm trying to isolate the code in fft.c which does the same thing.
That is, a fft that operates on time-domain data in time series.
I don't understand (yet) the LAME functions / interfaces and it seems there
are quite a few optimisation hacks which will make isolating the code
harder. Thus, any tips much appreciated...
Cheers
Simon
On Saturday, September 7, 2002, at 06:49 PM, Takehiro Tominaga wrote:
> Hi, ruffnex.
> I am looking forward to AltiVec optimized LAME :)
>
>>>>>> "r" == ruffnex <[EMAIL PROTECTED]> writes:
>
> r> After gprof'ing Lame 3.92, and looking at the source, I think
> r> fht.c might be an ideal candidate for vectorising with OSX's
> r> Altivec optimised DSP library.
>
> Yes, the code is easy to optimize with the SIMD instructions
> but currently, only 3DNow!-ed code is available which I ported from GOGO.
>
> r> (1) Function arguments
>
> r> static void fht(FLOAT *fz, int n)
> r> *fz = ptr to time-domain data (in what order ?)
>
> the order is 'bit-reversed series order'.
> See the fft_short() and fft_long() functions in fft.c for the details.
>
> r> n = the size of the input data to transform e.g. n-point dft
> r> (what is the valid range for n ?)
>
> only 256 or 1024.
>
> r> (2) the function is in-place (that is, the input data is
> r> over-written by the output data)
>
> yes, you are right. the calculation is done by in-place algorithm.
> --
> Takehiro TOMINAGA // may the source be with you!
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