Commit Graph

17 Commits

Author SHA1 Message Date
Andreas Rheinhardt
d75c4cc7c1 avutil/tx: Fix documentation of av_tx_uninit()
Adapt it to the actual (sane) behaviour.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
2022-02-11 19:38:41 +01:00
Lynne
af94ab7c7c
lavu/tx: add an RDFT implementation
RDFTs are full of conventions that vary between implementations.
What I've gone for here is what's most common between
both fftw, avcodec's rdft and what we use, the equivalent of
which is DFT_R2C for forward and IDFT_C2R for inverse. The
other 2 conventions (IDFT_R2C and DFT_C2R) were not used at
all in our code, and their names are also not appropriate.
If there's a use for either, we can easily add a flag which
would just flip the sign on one exptab.

For some unknown reason, possibly to allow reusing FFT's exp tables,
av_rdft's C2R output is 0.5x lower than what it should be to ensure
a proper back-and-forth conversion.
This code outputs its real samples at the correct level, which
matches FFTW's level, and allows the user to change the level
and insert arbitrary multiplies for free by setting the scale option.
2022-01-26 04:12:46 +01:00
Lynne
ef4bd81615
lavu/tx: rewrite internal code as a tree-based codelet constructor
This commit rewrites the internal transform code into a constructor
that stitches transforms (codelets).
This allows for transforms to reuse arbitrary parts of other
transforms, and allows transforms to be stacked onto one
another (such as a full iMDCT using a half-iMDCT which in turn
uses an FFT). It also permits for each step to be individually
replaced by assembly or a custom implementation (such as an ASIC).
2022-01-26 04:12:44 +01:00
Lynne
c14976be04
lavu/tx: improve documentation for existing transforms 2022-01-26 04:12:37 +01:00
Lynne
0072a42388
lavu/tx: add full-sized iMDCT transform flag 2021-04-24 17:17:27 +02:00
Lynne
aa6c757d50
lavu/tx: add unaligned flag to the API 2021-04-24 17:17:26 +02:00
Lynne
aa910a7ecd
lavu/tx: minor code style improvements and additional comments 2021-04-24 17:17:15 +02:00
Lynne
10341743d2
lavu/tx: require output argument to match input for inplace transforms
This simplifies some assembly code by a lot, by either saving a branch
or saving an entire duplicated function.
2021-02-26 05:42:24 +01:00
Lynne
5ca40d6d94
lavu/tx: support in-place FFT transforms
This commit adds support for in-place FFT transforms. Since our
internal transforms were all in-place anyway, this only changes
the permutation on the input.

Unfortunately, research papers were of no help here. All focused
on dry hardware implementations, where permutes are free, or on
software implementations where binary bloat is of no concern so
storing dozen times the transforms for each permutation and version
is not considered bad practice.
Still, for a pure C implementation, it's only around 28% slower
than the multi-megabyte FFTW3 in unaligned mode.

Unlike a closed permutation like with PFA, split-radix FFT bit-reversals
contain multiple NOPs, multiple simple swaps, and a few chained swaps,
so regular single-loop single-state permute loops were not possible.
Instead, we filter out parts of the input indices which are redundant.
This allows for a single branch, and with some clever AVX512 asm,
could possibly be SIMD'd without refactoring.

The inplace_idx array is guaranteed to never be larger than the
revtab array, and in practice only requires around log2(len) entries.

The power-of-two MDCTs can be done in-place as well. And it's
possible to eliminate a copy in the compound MDCTs too, however
it'll be slower than doing them out of place, and we'd need to dirty
the input array.
2021-02-21 17:05:16 +01:00
Lynne
aa34e99f88
lavu/tx: space out enum AVTXType values with newlines
Makes separation clearer.
2021-02-21 17:05:04 +01:00
Lynne
06a8596825
lavu: support arbitrary-point FFTs and all even (i)MDCT transforms
This patch adds support for arbitrary-point FFTs and all even MDCT
transforms.
Odd MDCTs are not supported yet as they're based on the DCT-II and DCT-III
and they're very niche.

With this we can now write tests.
2021-01-13 17:34:13 +01:00
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
9f494d1397 lavu/tx: improve documentation 2020-03-23 21:26:25 +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
d500eff3cc lavu/tx: mention FFT output is not normalized
Not even FFTW's output is normalized.
This should prevent at least some users from complaining that doing a forward
transform followed by an inverse transform has a mismatching output to the
original input.
2020-02-08 23:11:29 +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
Lynne
b79b29ddb1 libavutil: add an FFT & MDCT implementation
This commit adds a new API to libavutil to allow for arbitrary transformations
on various types of data.
This is a partly new implementation, with the power of two transforms taken
from libavcodec/fft_template, the 5 and 15-point FFT taken from mdct15, while
the 3-point FFT was written from scratch.
The (i)mdct folding code is taken from mdct15 as well, as the mdct_template
code was somewhat old, messy and not easy to separate.

A notable feature of this implementation is that it allows for 3xM and 5xM
based transforms, where M is a power of two, e.g. 384, 640, 768, 1280, etc.
AC-4 uses 3xM transforms while Siren uses 5xM transforms, so the code will
allow for decoding of such streams.
A non-exaustive list of supported sizes:
4, 8, 12, 16, 20, 24, 32, 40, 48, 60, 64, 80, 96, 120, 128, 160, 192, 240,
256, 320, 384, 480, 512, 640, 768, 960, 1024, 1280, 1536, 1920, 2048, 2560...

The API was designed such that it allows for not only 1D transforms but also
2D transforms of certain block sizes. This was partly on accident as the stride
argument is required for Opus MDCTs, but can be used in the context of a 2D
transform as well.
Also, various data types would be implemented eventually as well, such as
"double" and "int32_t".

Some performance comparisons with libfftw3f (SIMD disabled for both):
120:
  22353 decicycles in     fftwf_execute,     1024 runs,      0 skips
  21836 decicycles in compound_fft_15x8,     1024 runs,      0 skips

128:
  22003 decicycles in       fftwf_execute,   1024 runs,      0 skips
  23132 decicycles in monolithic_fft_ptwo,   1024 runs,      0 skips

384:
  75939 decicycles in      fftwf_execute,    1024 runs,      0 skips
  73973 decicycles in compound_fft_3x128,    1024 runs,      0 skips

640:
 104354 decicycles in       fftwf_execute,   1024 runs,      0 skips
 149518 decicycles in compound_fft_5x128,    1024 runs,      0 skips

768:
 109323 decicycles in      fftwf_execute,    1024 runs,      0 skips
 164096 decicycles in compound_fft_3x256,    1024 runs,      0 skips

960:
 186210 decicycles in      fftwf_execute,    1024 runs,      0 skips
 215256 decicycles in compound_fft_15x64,    1024 runs,      0 skips

1024:
 163464 decicycles in       fftwf_execute,   1024 runs,      0 skips
 199686 decicycles in monolithic_fft_ptwo,   1024 runs,      0 skips

With SIMD we should be faster than fftw for 15xM transforms as our fft15 SIMD
is around 2x faster than theirs, even if our ptwo SIMD is slightly slower.

The goal is to remove the libavcodec/mdct15 code and deprecate the
libavcodec/avfft interface once aarch64 and x86 SIMD code has been ported.
New code throughout the project should use this API.

The implementation passes fate when used in Opus, AAC and Vorbis, and the output
is identical with ATRAC9 as well.
2019-05-15 17:39:59 +01:00