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Use plain upsampling if merged isn't accelerated

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Currently, this only affects ARM, since it is the only platform that
accelerates YCbCr-to-RGB conversion but not merged upsampling.  Even if
"plain" upsampling isn't accelerated, the combination of accelerated
color conversion + unaccelerated plain upsampling is still faster than
the unaccelerated merged upsampling algorithms.

Closes #81
This commit is contained in:
DRC
2016-07-13 20:39:11 -05:00
parent 628c168c86
commit 7723d7f7d0
2 changed files with 19 additions and 0 deletions
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7
ChangeLog.md
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@@ -48,6 +48,13 @@ conformance issue.
rotating or transposing JPEG images that use 4:2:2 (h2v1) chroma subsampling.
The h1v2 fancy upsampling algorithm is not currently SIMD-accelerated.
5. If merged upsampling isn't SIMD-accelerated but YCbCr-to-RGB conversion is,
then libjpeg-turbo will now disable merged upsampling when decompressing YCbCr
JPEG images into RGB or extended RGB output images. This significantly speeds
up the decompression of 4:2:0 and 4:2:2 JPEGs on ARM platforms if fancy
upsampling is not used (for example, if the `-nosmooth` option to djpeg is
specified.)
1.5.0
=====

12
jdmaster.c
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@@ -22,6 +22,7 @@
#include "jpeglib.h"
#include "jpegcomp.h"
#include "jdmaster.h"
#include "jsimd.h"
/*
@@ -69,6 +70,17 @@ use_merged_upsample (j_decompress_ptr cinfo)
cinfo->comp_info[1]._DCT_scaled_size != cinfo->_min_DCT_scaled_size ||
cinfo->comp_info[2]._DCT_scaled_size != cinfo->_min_DCT_scaled_size)
return FALSE;
#ifdef WITH_SIMD
/* If YCbCr-to-RGB color conversion is SIMD-accelerated but merged upsampling
isn't, then disabling merged upsampling is likely to be faster when
decompressing YCbCr JPEG images. */
if (!jsimd_can_h2v2_merged_upsample() && !jsimd_can_h2v1_merged_upsample() &&
jsimd_can_ycc_rgb() && cinfo->jpeg_color_space == JCS_YCbCr &&
(cinfo->out_color_space == JCS_RGB ||
(cinfo->out_color_space >= JCS_EXT_RGB &&
cinfo->out_color_space <= JCS_EXT_ARGB)))
return FALSE;
#endif
/* ??? also need to test for upsample-time rescaling, when & if supported */
return TRUE; /* by golly, it'll work... */
#else