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Commit Graph

6 Commits

Author SHA1 Message Date
Lynne
2465fe1302 lavu/tx: add 2-point FFT transform
By itself, this allows 6-point, 10-point and 30-point transforms.
When the 9-point transform is added it allows for 18-point FFT,
and also for a 36-point MDCT (used by MP3).
2020-03-23 21:26:25 +00:00
Lynne
e1c84856bb lavu/tx: improve 3-point fixed precision
There's just no reason not to when its so easy (albeit messy) and its also
reducing the precision of all non-power-of-two transforms that use it.
2020-02-14 19:58:14 +00:00
Lynne
223b58c74b lavu/tx: slightly optimize fft15
Saves 2 additions.
2020-02-13 17:11:30 +00:00
Lynne
a38c6f47c9 lavu/tx: undef the correct macro
It was renamed and no warning was given for undeffing a nonexisting one.
2020-02-13 17:11:30 +00:00
Lynne
e8f054b095 lavu/tx: implement 32 bit fixed point FFT and MDCT
Required minimal changes to the code so made sense to implement.
FFT and MDCT tested, the output of both was properly rounded.
Fun fact: the non-power-of-two fixed-point FFT and MDCT are the fastest ever
non-power-of-two fixed-point FFT and MDCT written.
This can replace the power of two integer MDCTs in aac and ac3 if the
MIPS optimizations are ported across.
Unfortunately the ac3 encoder uses a 16-bit fixed point forward transform,
unlike the encoder which uses a 32bit inverse transform, so some modifications
might be required there.

The 3-point FFT is somewhat less accurate than it otherwise could be,
having minor rounding errors with bigger transforms. However, this
could be improved later, and the way its currently written is the way one
would write assembly for it.
Similar rounding errors can also be found throughout the power of two FFTs
as well, though those are more difficult to correct.
Despite this, the integer transforms are more than accurate enough.
2020-02-13 17:10:34 +00:00
Lynne
42e2319ba9 lavu/tx: add support for double precision FFT and MDCT
Simply moves and templates the actual transforms to support an
additional data type.
Unlike the float version, which is equal or better than libfftw3f,
double precision output is bit identical with libfftw3.
2019-08-02 01:19:52 +01:00