From: Carl Hetherington <cth@carlh.net>
Date: Mon, 16 Nov 2020 22:56:11 +0000 (+0100)
Subject: Use 64-byte alignment for aligned image memory.
X-Git-Tag: v2.15.108~49
X-Git-Url: https://main.carlh.net/gitweb/?p=dcpomatic.git;a=commitdiff_plain;h=fcc0515087a0b2bf9af5043af1c324367f1c152c

Use 64-byte alignment for aligned image memory.

FFmpeg uses this values if AVX512 is available, and with only
32-byte alignment I am seeing strange scaling effects whereby
crop_scale_window_test7 gives black bars down the right side of
cropped images (when run on an i7 7700).
---

diff --git a/src/lib/image.cc b/src/lib/image.cc
index 9dae94f7c..2d3a4a1d5 100644
--- a/src/lib/image.cc
+++ b/src/lib/image.cc
@@ -55,6 +55,11 @@ using std::runtime_error;
 using boost::shared_ptr;
 using dcp::Size;
 
+
+/** The memory alignment, in bytes, used for each row of an image if aligment is requested */
+#define ALIGNMENT 64
+
+
 int
 Image::vertical_factor (int n) const
 {
@@ -838,7 +843,7 @@ Image::bytes_per_pixel (int c) const
  *
  *  @param p Pixel format.
  *  @param s Size in pixels.
- *  @param aligned true to make each row of this image aligned to a 32-byte boundary.
+ *  @param aligned true to make each row of this image aligned to a ALIGNMENT-byte boundary.
  */
 Image::Image (AVPixelFormat p, dcp::Size s, bool aligned)
 	: _size (s)
@@ -862,7 +867,7 @@ Image::allocate ()
 
 	for (int i = 0; i < planes(); ++i) {
 		_line_size[i] = ceil (_size.width * bytes_per_pixel(i));
-		_stride[i] = stride_round_up (i, _line_size, _aligned ? 32 : 1);
+		_stride[i] = stride_round_up (i, _line_size, _aligned ? ALIGNMENT : 1);
 
 		/* The assembler function ff_rgb24ToY_avx (in libswscale/x86/input.asm)
 		   uses a 16-byte fetch to read three bytes (R/G/B) of image data.
@@ -875,7 +880,7 @@ Image::allocate ()
 
 		   Further to the above, valgrind is now telling me that ff_rgb24ToY_ssse3
 		   over-reads by more then _avx.  I can't follow the code to work out how much,
-		   so I'll just over-allocate by 32 bytes and have done with it.  Empirical
+		   so I'll just over-allocate by ALIGNMENT bytes and have done with it.  Empirical
 		   testing suggests that it works.
 
 		   In addition to these concerns, we may read/write as much as a whole extra line
@@ -901,12 +906,12 @@ Image::allocate ()
 		   |XXXwrittenXXX|<------line-size------------->|XXXwrittenXXXXXXwrittenXXX
 		                                                               ^^^^ out of bounds
 		*/
-		_data[i] = (uint8_t *) wrapped_av_malloc (_stride[i] * (sample_size(i).height + 1) + 32);
+		_data[i] = (uint8_t *) wrapped_av_malloc (_stride[i] * (sample_size(i).height + 1) + ALIGNMENT);
 #if HAVE_VALGRIND_MEMCHECK_H
 		/* The data between the end of the line size and the stride is undefined but processed by
 		   libswscale, causing lots of valgrind errors.  Mark it all defined to quell these errors.
 		*/
-		VALGRIND_MAKE_MEM_DEFINED (_data[i], _stride[i] * (sample_size(i).height + 1) + 32);
+		VALGRIND_MAKE_MEM_DEFINED (_data[i], _stride[i] * (sample_size(i).height + 1) + ALIGNMENT);
 #endif
 	}
 }
diff --git a/test/image_test.cc b/test/image_test.cc
index 6401db851..2f2c9a9b7 100644
--- a/test/image_test.cc
+++ b/test/image_test.cc
@@ -39,8 +39,8 @@ BOOST_AUTO_TEST_CASE (aligned_image_test)
 {
 	Image* s = new Image (AV_PIX_FMT_RGB24, dcp::Size (50, 50), true);
 	BOOST_CHECK_EQUAL (s->planes(), 1);
-	/* 160 is 150 aligned to the nearest 32 bytes */
-	BOOST_CHECK_EQUAL (s->stride()[0], 160);
+	/* 192 is 150 aligned to the nearest 64 bytes */
+	BOOST_CHECK_EQUAL (s->stride()[0], 192);
 	BOOST_CHECK_EQUAL (s->line_size()[0], 150);
 	BOOST_CHECK (s->data()[0]);
 	BOOST_CHECK (!s->data()[1]);
@@ -50,7 +50,7 @@ BOOST_AUTO_TEST_CASE (aligned_image_test)
 	/* copy constructor */
 	Image* t = new Image (*s);
 	BOOST_CHECK_EQUAL (t->planes(), 1);
-	BOOST_CHECK_EQUAL (t->stride()[0], 160);
+	BOOST_CHECK_EQUAL (t->stride()[0], 192);
 	BOOST_CHECK_EQUAL (t->line_size()[0], 150);
 	BOOST_CHECK (t->data()[0]);
 	BOOST_CHECK (!t->data()[1]);
@@ -67,7 +67,7 @@ BOOST_AUTO_TEST_CASE (aligned_image_test)
 	Image* u = new Image (AV_PIX_FMT_YUV422P, dcp::Size (150, 150), false);
 	*u = *s;
 	BOOST_CHECK_EQUAL (u->planes(), 1);
-	BOOST_CHECK_EQUAL (u->stride()[0], 160);
+	BOOST_CHECK_EQUAL (u->stride()[0], 192);
 	BOOST_CHECK_EQUAL (u->line_size()[0], 150);
 	BOOST_CHECK (u->data()[0]);
 	BOOST_CHECK (!u->data()[1]);