[FFmpeg-devel] [PATCH] avutil: Move av_rint64_clip_* to internal.h

[Ganesh Ajjanagadde]

On Sun, Nov 15, 2015 at 11:00 AM, Michael Niedermayer
<michael at niedermayer.cc> wrote:
> On Sun, Nov 15, 2015 at 10:24:52AM -0500, Ganesh Ajjanagadde wrote:
>> On Sun, Nov 15, 2015 at 10:23 AM, wm4 <nfxjfg at gmail.com> wrote:
>> > On Sun, 15 Nov 2015 10:20:41 -0500
>> > Ganesh Ajjanagadde <gajjanag at mit.edu> wrote:
>> >
>> >> On Sat, Nov 14, 2015 at 9:01 PM, James Almer <jamrial at gmail.com> wrote:
>> >> > On 11/14/2015 10:48 PM, Michael Niedermayer wrote:
>> >> >> From: Michael Niedermayer <michael at niedermayer.cc>
>> >> >>
>> >> >> This should avoid build failures on VS2012
>> >> >> Feel free to changes this to a different solution
>> >> >>
>> >> >> Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
>> >> >> ---
>> >> >>  libavutil/common.h   |   39 ---------------------------------------
>> >> >>  libavutil/internal.h |   40 ++++++++++++++++++++++++++++++++++++++++
>> >> >>  2 files changed, 40 insertions(+), 39 deletions(-)
>> >> >>
>> >> >> diff --git a/libavutil/common.h b/libavutil/common.h
>> >> >> index 813fb37..6f0f582 100644
>> >> >> --- a/libavutil/common.h
>> >> >> +++ b/libavutil/common.h
>> >> >> @@ -298,42 +298,6 @@ 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)
>> >> >> @@ -547,9 +511,6 @@ 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/internal.h b/libavutil/internal.h
>> >> >> index 5c2cd99..cb0c8cd 100644
>> >> >> --- a/libavutil/internal.h
>> >> >> +++ b/libavutil/internal.h
>> >> >> @@ -257,6 +257,46 @@ void avpriv_request_sample(void *avc,
>> >> >>  #endif
>> >> >>
>> >> >>  /**
>> >> >> + * 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)
>> >> >
>> >> > IMO rename it to avpriv_rint64_clip() or even ff_rint64_clip() since it's inlined
>> >> > and not public/exported.
>> >>
>> >> Just noticed an issue: Ronald mentioned to me that ffserver and other
>> >> such programs should not use internal API. This therefore needs to be
>> >> exported somehow.
>> >
>> > If only ffserver needs it, implement it there?
>> >
>> > Or even better, just delete ffserver.
>>
>> I have repeated this many times in the past, but ffserver was given as
>> a mere illustration. cmdutils.c also needs it, and there are likely
>> more such instances that I have not checked.
>
> i think both cmdutils and ffserver should check their arguments
> and not clip them
> this can not be done after *rint64_clip() in all cases because
> if the whole int64 range is valid then there is not enough information
> left.
> If the check is done before on the doubles then normal llrint() should
> work for these cases.

Such checks will be ugly, since direct llrint on a value out of range
is undefined. Essentially the checks of the style of the clip function
need to be done.

> ff_rint64_clip() might still be usefull elsewhere but i think all
> user supplied values should be checked and not clipped

It is subjective to me. I personally think that if a user supplies e.g
INT64_MAX + 1, one should not simply fail. Clipping to the range of
the integer is a best effort solution. Diagnostics can be added, but
it is a separate issue.

>
> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> No great genius has ever existed without some touch of madness. -- Aristotle
>
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