[FFmpeg-devel] [PATCHv4] avutil/common: add av_rint64_clip

[Ganesh Ajjanagadde]

The rationale for this function is reflected in the documentation for
it, and is copied here:

Clip a double value into the long long amin-amax range.
This function is needed because conversion of floating point to integers when
it does not fit in the integer's representation does not necessarily saturate
correctly (usually converted to a cvttsd2si on x86) which saturates numbers
> INT64_MAX to INT64_MIN. The standard marks such conversions as undefined
behavior, allowing this sort of mathematically bogus conversions. This provides
a safe alternative that is slower obviously but assures safety and better
mathematical behavior.
API:
@param a value to clip
@param amin minimum value of the clip range
@param amax maximum value of the clip range
@return clipped value

Note that a priori if one can guarantee from the calling side that the
double is in range, it is safe to simply do an explicit/implicit cast,
and that will be far faster. However, otherwise this function should be
used.

avutil minor version is bumped.

Reviewed-by: Ronald S. Bultje <rsbultje at gmail.com>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
---
 libavutil/common.h  | 30 ++++++++++++++++++++++++++++++
 libavutil/version.h |  2 +-
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/libavutil/common.h b/libavutil/common.h
index 6f0f582..f4687ab 100644
--- a/libavutil/common.h
+++ b/libavutil/common.h
@@ -298,6 +298,33 @@ static av_always_inline av_const double av_clipd_c(double a, double amin, double
     else               return a;
 }
 
+/**
+ * Clip and convert a double value into the long long amin-amax range.
+ * This function is needed because conversion of floating point to integers when
+ * it does not fit in the integer's representation does not necessarily saturate
+ * correctly (usually converted to a cvttsd2si on x86) which saturates numbers
+ * > INT64_MAX to INT64_MIN. The standard marks such conversions as undefined
+ * behavior, allowing this sort of mathematically bogus conversions. This provides
+ * a safe alternative that is slower obviously but assures safety and better
+ * mathematical behavior.
+ * @param a value to clip
+ * @param amin minimum value of the clip range
+ * @param amax maximum value of the clip range
+ * @return clipped value
+ */
+static av_always_inline av_const int64_t av_rint64_clip_c(double a, int64_t amin, int64_t amax)
+{
+#if defined(HAVE_AV_CONFIG_H) && defined(ASSERT_LEVEL) && ASSERT_LEVEL >= 2
+    if (amin > amax) abort();
+#endif
+    // INT64_MAX+1,INT64_MIN are exactly representable as IEEE doubles
+    if (a >=  9223372036854775808.0 || llrint(a) >= amax)
+        return amax;
+    if (a <= -9223372036854775808.0 || llrint(a) <= amin)
+        return amin;
+    return llrint(a);
+}
+
 /** Compute ceil(log2(x)).
  * @param x value used to compute ceil(log2(x))
  * @return computed ceiling of log2(x)
@@ -511,6 +538,9 @@ static av_always_inline av_const int av_popcount64_c(uint64_t x)
 #ifndef av_clipd
 #   define av_clipd         av_clipd_c
 #endif
+#ifndef av_rint64_clip
+#   define av_rint64_clip   av_rint64_clip_c
+#endif
 #ifndef av_popcount
 #   define av_popcount      av_popcount_c
 #endif
diff --git a/libavutil/version.h b/libavutil/version.h
index 909f9a6..bcad658 100644
--- a/libavutil/version.h
+++ b/libavutil/version.h
@@ -56,7 +56,7 @@
  */
 
 #define LIBAVUTIL_VERSION_MAJOR  55
-#define LIBAVUTIL_VERSION_MINOR   5
+#define LIBAVUTIL_VERSION_MINOR   6
 #define LIBAVUTIL_VERSION_MICRO 100
 
 #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \
-- 
2.6.2