[FFmpeg-devel] [PATCH] Optimize pure C unscaled yuv2rgb.

Reimar Döffinger Reimar.Doeffinger at gmx.de
Fri Oct 25 22:49:07 CEST 2013

Aligning the tables reduces the amount of code generated on
e.g. ARM as the offset constant then has few enough set bits
so it can be encoded inside a single instruction instead of 2.
Ideally all should be declared aligned, but the DECLARE_ALIGNED
macros does not work with pointer tables, thus also reordered
the tables.

Signed-off-by: Reimar Döffinger <Reimar.Doeffinger at gmx.de>
 libswscale/swscale_internal.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/libswscale/swscale_internal.h b/libswscale/swscale_internal.h
index 33fdfc2..6ad278e 100644
--- a/libswscale/swscale_internal.h
+++ b/libswscale/swscale_internal.h
@@ -362,9 +362,11 @@ typedef struct SwsContext {
     int dstY;                     ///< Last destination vertical line output from last slice.
     int flags;                    ///< Flags passed by the user to select scaler algorithm, optimizations, subsampling, etc...
     void *yuvTable;             // pointer to the yuv->rgb table start so it can be freed()
+    // alignment ensures the offset can be added in a single
+    // instruction on e.g. ARM
+    DECLARE_ALIGNED(16, int, table_gV)[256 + 2*YUVRGB_TABLE_HEADROOM];
     uint8_t *table_rV[256 + 2*YUVRGB_TABLE_HEADROOM];
     uint8_t *table_gU[256 + 2*YUVRGB_TABLE_HEADROOM];
-    int table_gV[256 + 2*YUVRGB_TABLE_HEADROOM];
     uint8_t *table_bU[256 + 2*YUVRGB_TABLE_HEADROOM];
     DECLARE_ALIGNED(16, int32_t, input_rgb2yuv_table)[16+40*4]; // This table can contain both C and SIMD formatted values, teh C vales are always at the XY_IDX points
 #define RY_IDX 0

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