avfilter/vf_lut3d: add x86-optimized tetrahedral interpolation

I spotted an interesting pattern that I didn't see before that leads to the implementation being faster.
The bit shifting table I was using before is no longer needed, and was able to remove quite a few lines. 
I also add use of FMA on the AVX2 version.

f32 1920x1080 1 thread with prelut
c impl
1434012700 UNITS in lut3d->interp,       1 runs,      0 skips
1434035335 UNITS in lut3d->interp,       2 runs,      0 skips
1423615347 UNITS in lut3d->interp,       4 runs,      0 skips
1426268863 UNITS in lut3d->interp,       8 runs,      0 skips

sse2
905484420 UNITS in lut3d->interp,       1 runs,      0 skips
905659010 UNITS in lut3d->interp,       2 runs,      0 skips
915167140 UNITS in lut3d->interp,       4 runs,      0 skips
915834222 UNITS in lut3d->interp,       8 runs,      0 skips

avx
574794860 UNITS in lut3d->interp,       1 runs,      0 skips
581035090 UNITS in lut3d->interp,       2 runs,      0 skips
584116720 UNITS in lut3d->interp,       4 runs,      0 skips
581460290 UNITS in lut3d->interp,       8 runs,      0 skips

avx2
301698880 UNITS in lut3d->interp,       1 runs,      0 skips
301982880 UNITS in lut3d->interp,       2 runs,      0 skips
306962430 UNITS in lut3d->interp,       4 runs,      0 skips
305472025 UNITS in lut3d->interp,       8 runs,      0 skips

gbrap16 1920x1080 1 thread with prelut
c impl
1480894840 UNITS in lut3d->interp,       1 runs,      0 skips
1502922990 UNITS in lut3d->interp,       2 runs,      0 skips
1496114307 UNITS in lut3d->interp,       4 runs,      0 skips
1492554551 UNITS in lut3d->interp,       8 runs,      0 skips

sse2
980777180 UNITS in lut3d->interp,       1 runs,      0 skips
986121520 UNITS in lut3d->interp,       2 runs,      0 skips
986489840 UNITS in lut3d->interp,       4 runs,      0 skips
998832248 UNITS in lut3d->interp,       8 runs,      0 skips

avx
622212360 UNITS in lut3d->interp,       1 runs,      0 skips
622981160 UNITS in lut3d->interp,       2 runs,      0 skips
645396315 UNITS in lut3d->interp,       4 runs,      0 skips
641057075 UNITS in lut3d->interp,       8 runs,      0 skips

avx2
321336400 UNITS in lut3d->interp,       1 runs,      0 skips
321268920 UNITS in lut3d->interp,       2 runs,      0 skips
323459895 UNITS in lut3d->interp,       4 runs,      0 skips
324949967 UNITS in lut3d->interp,       8 runs,      0 skips

1 files changed, 83 insertions, 0 deletions

diff --git a/libavfilter/lut3d.h b/libavfilter/lut3d.h
new file mode 100644
index 0000000000..bc32eac91c
--- /dev/null
+++ b/libavfilter/lut3d.h
@@ -0,0 +1,83 @@
+/*
+ * Copyright (c) 2013 Clément Bœsch
+ * Copyright (c) 2018 Paul B Mahol
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+#ifndef AVFILTER_LUT3D_H
+#define AVFILTER_LUT3D_H
+
+#include "libavutil/pixdesc.h"
+#include "framesync.h"
+#include "avfilter.h"
+
+enum interp_mode {
+    INTERPOLATE_NEAREST,
+    INTERPOLATE_TRILINEAR,
+    INTERPOLATE_TETRAHEDRAL,
+    INTERPOLATE_PYRAMID,
+    INTERPOLATE_PRISM,
+    NB_INTERP_MODE
+};
+
+struct rgbvec {
+    float r, g, b;
+};
+
+/* 3D LUT don't often go up to level 32, but it is common to have a Hald CLUT
+ * of 512x512 (64x64x64) */
+#define MAX_LEVEL 256
+#define PRELUT_SIZE 65536
+
+typedef struct Lut3DPreLut {
+    int size;
+    float min[3];
+    float max[3];
+    float scale[3];
+    float* lut[3];
+} Lut3DPreLut;
+
+typedef struct LUT3DContext {
+    const AVClass *class;
+    struct rgbvec *lut;
+    int lutsize;
+    int lutsize2;
+    struct rgbvec scale;
+    int interpolation;          ///<interp_mode
+    char *file;
+    uint8_t rgba_map[4];
+    int step;
+    avfilter_action_func *interp;
+    Lut3DPreLut prelut;
+#if CONFIG_HALDCLUT_FILTER
+    uint8_t clut_rgba_map[4];
+    int clut_step;
+    int clut_bits;
+    int clut_planar;
+    int clut_float;
+    int clut_width;
+    FFFrameSync fs;
+#endif
+} LUT3DContext;
+
+typedef struct ThreadData {
+    AVFrame *in, *out;
+} ThreadData;
+
+void ff_lut3d_init_x86(LUT3DContext *s, const AVPixFmtDescriptor *desc);
+
+#endif /* AVFILTER_LUT3D_H */