[FFmpeg-devel] [PATCH v2] cpu: add a function for querying maximum required data alignment

[James Almer]

From: Anton Khirnov <anton at khirnov.net>

(cherry picked from commit e6bff23f1e11aefb16a2b5d6ee72bf7469c5a66e)
Signed-off-by: James Almer <jamrial at gmail.com>
---
This is (afaics) the last API introduced to libav before the major bump.

Now checking all the x86 flags that would require aligment of 16 bytes
or more.

 doc/APIchanges      |  3 +++
 libavutil/cpu.c     | 35 +++++++++++++++++++++++++++++++++++
 libavutil/cpu.h     | 13 +++++++++++++
 libavutil/version.h |  2 +-
 4 files changed, 52 insertions(+), 1 deletion(-)

diff --git a/doc/APIchanges b/doc/APIchanges
index 4effbf9364..6a57c210a9 100644
--- a/doc/APIchanges
+++ b/doc/APIchanges
@@ -15,6 +15,9 @@ libavutil:     2015-08-28
 
 API changes, most recent first:
 
+2017-09-xx - xxxxxxx - lavu 55.75.100 / lavu 55.31.0 - cpu.h
+  Add av_cpu_max_align() for querying maximum required data alignment.
+
 2017-09-01 - xxxxxxx - lavf 57.81.100 - avio.h
   Add avio_read_partial().
 
diff --git a/libavutil/cpu.c b/libavutil/cpu.c
index a22da0fa8c..4f04da2460 100644
--- a/libavutil/cpu.c
+++ b/libavutil/cpu.c
@@ -16,9 +16,11 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#include <stddef.h>
 #include <stdint.h>
 #include <stdatomic.h>
 
+#include "attributes.h"
 #include "cpu.h"
 #include "cpu_internal.h"
 #include "config.h"
@@ -299,3 +301,36 @@ int av_cpu_count(void)
 
     return nb_cpus;
 }
+
+size_t av_cpu_max_align(void)
+{
+    int av_unused flags = av_get_cpu_flags();
+
+#if ARCH_ARM || ARCH_AARCH64
+    if (flags & AV_CPU_FLAG_NEON)
+        return 16;
+#elif ARCH_PPC
+    if (flags & AV_CPU_FLAG_ALTIVEC)
+        return 16;
+#elif ARCH_X86
+    if (flags & (AV_CPU_FLAG_AVX2     |
+                 AV_CPU_FLAG_AVX      |
+                 AV_CPU_FLAG_FMA4     |
+                 AV_CPU_FLAG_FMA3))
+        return 32;
+    if (flags & (AV_CPU_FLAG_XOP      |
+                 AV_CPU_FLAG_AESNI    |
+                 AV_CPU_FLAG_SSE42    |
+                 AV_CPU_FLAG_SSE4     |
+                 AV_CPU_FLAG_SSSE3    |
+                 AV_CPU_FLAG_SSE3     |
+                 AV_CPU_FLAG_SSE2     |
+                 AV_CPU_FLAG_SSE      |
+                 AV_CPU_FLAG_AVXSLOW  |
+                 AV_CPU_FLAG_SSE3SLOW |
+                 AV_CPU_FLAG_SSE2SLOW))
+        return 16;
+#endif
+
+    return 8;
+}
diff --git a/libavutil/cpu.h b/libavutil/cpu.h
index de05593446..9e5d40affe 100644
--- a/libavutil/cpu.h
+++ b/libavutil/cpu.h
@@ -21,6 +21,8 @@
 #ifndef AVUTIL_CPU_H
 #define AVUTIL_CPU_H
 
+#include <stddef.h>
+
 #include "attributes.h"
 
 #define AV_CPU_FLAG_FORCE    0x80000000 /* force usage of selected flags (OR) */
@@ -113,4 +115,15 @@ int av_parse_cpu_caps(unsigned *flags, const char *s);
  */
 int av_cpu_count(void);
 
+/**
+ * Get the maximum data alignment that may be required by FFmpeg.
+ *
+ * Note that this is affected by the build configuration and the CPU flags mask,
+ * so e.g. if the CPU supports AVX, but libavutil has been built with
+ * --disable-avx or the AV_CPU_FLAG_AVX flag has been disabled through
+ *  av_set_cpu_flags_mask(), then this function will behave as if AVX is not
+ *  present.
+ */
+size_t av_cpu_max_align(void);
+
 #endif /* AVUTIL_CPU_H */
diff --git a/libavutil/version.h b/libavutil/version.h
index 6e25b4690c..d99eff5d15 100644
--- a/libavutil/version.h
+++ b/libavutil/version.h
@@ -80,7 +80,7 @@
 
 
 #define LIBAVUTIL_VERSION_MAJOR  55
-#define LIBAVUTIL_VERSION_MINOR  74
+#define LIBAVUTIL_VERSION_MINOR  75
 #define LIBAVUTIL_VERSION_MICRO 100
 
 #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \
-- 
2.13.3