avutil/common: add av_rint64_clip

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@gmail.com>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
This commit is contained in:
Ganesh Ajjanagadde 2015-11-01 09:33:29 -05:00
parent df91aa034b
commit 6f520ce1a6
2 changed files with 40 additions and 1 deletions

View File

@ -298,6 +298,42 @@ 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)
{
int64_t res;
#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
// do range checks first
if (a >= 9223372036854775808.0)
return amax;
if (a <= -9223372036854775808.0)
return amin;
// safe to call llrint and clip accordingly
res = llrint(a);
if (res > amax)
return amax;
if (res < amin)
return amin;
return res;
}
/** Compute ceil(log2(x)).
* @param x value used to compute ceil(log2(x))
* @return computed ceiling of log2(x)
@ -511,6 +547,9 @@ 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

View File

@ -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, \