and optimize average, grainextract, multiply, screen, grain merge

Blend function speedups on x86_64 Core i5 4460:

ffmpeg -f lavfi -i allyuv -vf framerate=60:threads=1 -f null none

C:     447548411 decicycles in Blend,    2048 runs,      0 skips
SSSE3: 130020087 decicycles in Blend,    2048 runs,      0 skips
AVX2:  128508221 decicycles in Blend,    2048 runs,      0 skips

ffmpeg -f lavfi -i allyuv -vf format=yuv420p12,framerate=60:threads=1 -f null none

C:     228932745 decicycles in Blend,    2048 runs,      0 skips
SSE4:  123357781 decicycles in Blend,    2048 runs,      0 skips
AVX2:  121215353 decicycles in Blend,    2048 runs,      0 skips

Signed-off-by: Marton Balint <cus@passwd.hu>

This reverts commits 1a5865b6dc and
8fb1d63d91.

They made fate interlace tests fail when AVX2 was used.

Signed-off-by: James Almer <jamrial@gmail.com>

based on patch by Paul B Mahol

related to ticket 6491

ticket 6491

Signed-off-by: James Almer <jamrial@gmail.com>

Signed-off-by: James Almer <jamrial@gmail.com>

Signed-off-by: James Almer <jamrial@gmail.com>

Signed-off-by: Paul B Mahol <onemda@gmail.com>

Signed-off-by: Paul B Mahol <onemda@gmail.com>

Fixes building with yasm

Tested-by: stevenliu
Signed-off-by: James Almer <jamrial@gmail.com>

Signed-off-by: Paul B Mahol <onemda@gmail.com>

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Thomas Mundt <tmundt75@gmail.com>
Signed-off-by: James Almer <jamrial@gmail.com>

The complex vertical low-pass filter slightly over-sharpens the picture. This becomes visible when several transcodings are cascaded and the error potentises, e.g. some generations of HD->SD SD->HD.
To prevent this behaviour the destination pixel must not exceed the source pixel when the average of the pixels above and below is less than the source pixel. And the other way around.

Tested and approved in a visual transcoding cascade test by video professionals.
SSIM/PSNR test with the first generation of an HD->SD file as a reference against the 6th generation(3 x SD->HD HD->SD):
Results without the patch:
SSIM Y:0.956508 (13.615881) U:0.991601 (20.757750) V:0.993004 (21.551382) All:0.974405 (15.918463)
PSNR y:31.838009 u:48.424280 v:48.962711 average:34.759466 min:31.699297 max:40.857847
Results with the patch:
SSIM Y:0.970051 (15.236232) U:0.991883 (20.905857) V:0.993174 (21.658049) All:0.981290 (17.279202)
PSNR y:34.412108 u:48.504454 v:48.969496 average:37.264644 min:34.310637 max:42.373392

Signed-off-by: Thomas Mundt <tmundt75@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

Signed-off-by: James Almer <jamrial@gmail.com>

Signed-off-by: Paul B Mahol <onemda@gmail.com>

Process more pixels per loop.

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: James Almer <jamrial@gmail.com>

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: James Almer <jamrial@gmail.com>

None of them are specific to the YASM assembler.

(Cherry-picked from libav commit 39e208f4d4)

Signed-off-by: James Almer <jamrial@gmail.com>

Signed-off-by: Paul B Mahol <onemda@gmail.com>

This complex (-1 2 6 2 -1) filter slightly less reduces interlace 'twitter' but better retain detail and subjective sharpness impression compared to the linear (1 2 1) filter.

Signed-off-by: Thomas Mundt <tmundt75@gmail.com>
Signed-off-by: James Almer <jamrial@gmail.com>

Signed-off-by: Thomas Mundt <tmundt75@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

None of them are specific to the YASM assembler.

Signed-off-by: Paul B Mahol <onemda@gmail.com>

This fixes many warnings of the sort
warning: label alone on a line without a colon might be in error

Signed-off-by: James Almer <jamrial@gmail.com>

See merge commit '39d6d3618d48625decaff7d9bdbb45b44ef2a805'.

Fixes failures with yasm 1.1.0 and older

Signed-off-by: James Almer <jamrial@gmail.com>

Old yasm/nasm versions don't support some of these

Signed-off-by: James Almer <jamrial@gmail.com>

Signed-off-by: James Almer <jamrial@gmail.com>

on x86_64:
        time    PSNR
plain   3.303   inf
SSE     1.649   107.087535
SSE3    1.632   107.087535
AVX     1.409   106.986771
FMA3    1.265   107.108437

on x86_32 (PSNR compared to x86_64 plain):
        time    PSNR
plain   7.225   103.951979
SSE     1.827   105.859282
SSE3    1.819   105.859282
AVX     1.533   105.997661
FMA3    1.384   105.885377

FMA4 test is not available

Reviewed-by: James Almer <jamrial@gmail.com>
Signed-off-by: Muhammad Faiz <mfcc64@gmail.com>

Signed-off-by: Paul B Mahol <onemda@gmail.com>

Also add some documentation for each function to colorspacedsp.h.