Average vertically before horizontally; horizontal averaging is more
worksome. Doing the vertical averaging first reduces the number of
horizontal averages by half.
Use pmaddubsw and pavgw to do the horizontal averaging for a slight
performance improvement.
Minor tweaks.
Improve the SSSE3 dyadic downsample routines and drop the SSE4 routines.
The non-temporal loads used in the SSE4 routines do nothing for cache-
backed memory AFAIK.
Adjust tests because averaging vertically first gives slightly different
output.
~2.39x speedup for the widthx32 routine on Haswell when not memory-bound.
~2.20x speedup for the widthx16 routine on Haswell when not memory-bound.
Note that the widthx16 routine can be unrolled for further speedup.
Keep track of relative pixel offsets and utilize pshufb to efficiently
extract relevant pixels for horizontal scaling ratios <= 4.
Fall back to a generic approach for ratios > 4. Note that the generic
approach can be backported to SSE2.
The implementation assumes that data beyond the end of each line,
before the next line begins, can be dirtied; which AFAICT is safe with
the current usage of these routines.
Speedup is ~6.67x/~3.26x (32-bit/64-bit) for horizontal ratios <= 2,
~6.24x/~3.00x for ratios within (2, 4], and ~4.89x/~2.17x for ratios
> 4 when not memory-bound on Haswell as compared with the current SSE2
implementation.
WelsQuantFour4x4Max_avx2 (~2.06x speedup over SSE2)
WelsQuantFour4x4_avx2 (~2.32x speedup over SSE2)
WelsQuant4x4Dc_avx2 (~1.49x speedup over SSE2)
WelsQuant4x4_avx2 (~1.42x speedup over SSE2)
At lower bitrates, it is overall faster to conditionally do one block
at a time with SSE2 on Haswell and likely other common architectures.
At higher bitrates, it is faster to use the wider routine that IDCTs
four blocks at a time. To avoid potential performance regressions
as compared to MMX, stick with single-block IDCTs with SSE2. There
is still a performance advantage as compared to MMX because the
single-block SSE2 routine is faster than the corresponding MMX
routine.
Stick with four blocks at a time with AVX2 for which that appears
to be consistently faster on Haswell.
Move asm routines to common. Delete obsolete decoder routines.
Use wider routines where applicable.
~1.07x overall faster decode on a quick 720p30 4Mbps test on Haswell.
WelsSampleSatd16x16_avx2 (~2.31x speedup over SSE4.1 on Haswell).
WelsSampleSatd16x8_avx2 (~2.19x speedup over SSE4.1 on Haswell).
WelsSampleSatd8x16_avx2 (~1.68x speedup over SSE4.1 on Haswell).
WelsSampleSatd8x8_avx2 (~1.53x speedup over SSE4.1 on Haswell).
This reverts an unrelated part of e7e3b4f37f.
Since the function still is declared as taking an int32_t parameter
in the header, changing the function implementation makes it end
up as a different function.
