FFmpeg

Commit Graph

Author	SHA1	Message	Date
Michael Niedermayer	85b883429f	avutil/tx: avoid negative left shifts Fixes: left shift of negative value -1 Fixes: 33736/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SIREN_fuzzer-6657785795313664 Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>	4 years ago
Lynne	119a3f7e8d	lavu/x86: add FFT assembly This commit adds a pure x86 assembly SIMD version of the FFT in libavutil/tx. The design of this pure assembly FFT is pretty unconventional. On the lowest level, instead of splitting the complex numbers into real and imaginary parts, we keep complex numbers together but split them in terms of parity. This saves a number of shuffles in each transform, but more importantly, it splits each transform into two independent paths, which we process using separate registers in parallel. This allows us to keep all units saturated and lets us use all available registers to avoid dependencies. Moreover, it allows us to double the granularity of our per-load permutation, skipping many expensive lookups and allowing us to use just 4 loads per register, rather than 8, or in case FMA3 (and by extension, AVX2), use the vgatherdpd instruction, which is at least as fast as 4 separate loads on old hardware, and quite a bit faster on modern CPUs). Higher up, we go for a bottom-up construction of large transforms, foregoing the traditional per-transform call-return recursion chains. Instead, we always start at the bottom-most basis transform (in this case, a 32-point transform), and continue constructing larger and larger transforms until we return to the top-most transform. This way, we only touch the stack 3 times per a complete target transform: once for the 1/2 length transform and two times for the 1/4 length transform. The combination algorithm we use is a standard Split-Radix algorithm, as used in our C code. Although a version with less operations exists (Steven G. Johnson and Matteo Frigo's "A modified split-radix FFT with fewer arithmetic operations", IEEE Trans. Signal Process. 55 (1), 111–119 (2007), which is the one FFTW uses), it only has 2% less operations and requires at least 4x the binary code (due to it needing 4 different paths to do a single transform). That version also has other issues which prevent it from being implemented with SIMD code as efficiently, which makes it lose the marginal gains it offered, and cannot be performed bottom-up, requiring many recursive call-return chains, whose overhead adds up. We go through a lot of effort to minimize load/stores by keeping as much in registers in between construcring transforms. This saves us around 32 cycles, on paper, but in reality a lot more due to load/store aliasing (a load from a memory location cannot be issued while there's a store pending, and there are only so many (2 for Zen 3) load/store units in a CPU). Also, we interleave coefficients during the last stage to save on a store+load per register. Each of the smallest, basis transforms (4, 8 and 16-point in our case) has been extremely optimized. Our 8-point transform is barely 20 instructions in total, beating our old implementation 8-point transform by 1 instruction. Our 2x8-point transform is 23 instructions, beating our old implementation by 6 instruction and needing 50% less cycles. Our 16-point transform's combination code takes slightly more instructions than our old implementation, but makes up for it by requiring a lot less arithmetic operations. Overall, the transform was optimized for the timings of Zen 3, which at the time of writing has the most IPC from all documented CPUs. Shuffles were preferred over arithmetic operations due to their 1/0.5 latency/throughput. On average, this code is 30% faster than our old libavcodec implementation. It's able to trade blows with the previously-untouchable FFTW on small transforms, and due to its tiny size and better prediction, outdoes FFTW on larger transforms by 11% on the largest currently supported size.	4 years ago
Lynne	1978b143eb	checkasm: add av_tx FFT SIMD testing code This sadly required making changes to the code itself, due to the same context needing to be reused for both versions. The lookup table had to be duplicated for both versions.	4 years ago
Lynne	ff71671d88	lavu/tx: add parity revtab generator version This will be used for SIMD support.	4 years ago
Lynne	aa910a7ecd	lavu/tx: minor code style improvements and additional comments	4 years ago
Lynne	8e94b7cff0	lavu/tx: invert permutation lookups out[lut[i]] = in[i] lookups were 4.04 times(!) slower than out[i] = in[lut[i]] lookups for an out-of-place FFT of length 4096. The permutes remain unchanged for anything but out-of-place monolithic FFT, as those benefit quite a lot from the current order (it means there's only 1 lookup necessary to add to an offset, rather than a full gather). The code was based around non-power-of-two FFTs, so this wasn't benchmarked early on.	4 years ago
Lynne	9ddaf0c9f0	lavu/tx: simplify in-place permute search function	4 years ago
Andreas Rheinhardt	c7c7aa85b7	avutil/tx: Fix declaration after statement Reviewed-by: Paul B Mahol <onemda@gmail.com> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>	4 years ago
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.	4 years ago
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.	5 years ago
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.	5 years ago
Ruiling Song	65646db8e8	avutil/tx: should check against (*ctx) ctx is a pointer to pointer here. Signed-off-by: Ruiling Song <ruiling.song@intel.com>	6 years ago
Lynne	6044534964	avutil/tx: fix forward compound non-mod-15 based MDCTs There was a hardcoded value left. Wasn't caught earlier as no code uses compound forward mod-3/5 MDCTs yet.	6 years ago
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.	6 years ago

14 Commits (d0293c770bbc747ba8eaa310f7b3632207a36ebd)