On Sun, Nov 15, 2015 at 11:35:04AM -0500, Ganesh Ajjanagadde wrote:
> On Sun, Nov 15, 2015 at 11:19 AM, wm4 <nfx...@gmail.com> wrote:
> > On Sun, 15 Nov 2015 11:10:23 -0500
> > Ganesh Ajjanagadde <gajja...@mit.edu> wrote:
> >
> >> On Sun, Nov 15, 2015 at 11:00 AM, Michael Niedermayer
> >> <mich...@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 <nfx...@gmail.com> wrote:
> >> >> > On Sun, 15 Nov 2015 10:20:41 -0500
> >> >> > Ganesh Ajjanagadde <gajja...@mit.edu> wrote:
> >> >> >
> >> >> >> On Sat, Nov 14, 2015 at 9:01 PM, James Almer <jamr...@gmail.com>
> >> >> >> wrote:
> >> >> >> > On 11/14/2015 10:48 PM, Michael Niedermayer wrote:
> >> >> >> >> From: Michael Niedermayer <mich...@niedermayer.cc>
> >> >> >> >>
> >> >> >> >> This should avoid build failures on VS2012
> >> >> >> >> Feel free to changes this to a different solution
> >> >> >> >>
> >> >> >> >> Signed-off-by: Michael Niedermayer <mich...@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.
> >
> > But aren't these checks simple (as seen in the patch), or am I missing
> > something?
>
> They are simple, but out of context, it is unclear where the "magic"
> 922... comes from. Even worse, 922... does not do the range check by
> itself, but only corrects the undefined behavior. Separate range check
> will need to be done if one wants to get e.g INT_MIN to INT_MAX.
>
> At the cost of loss of context, one could add a log line at some level
> in the rint64_clip warning whenever the value is clipped. I personally
> would favor that.
i dont think a warning log alone is a good idea, this can be a problem
for example for GUI user apps which dont show the log in a vissible
enough way
about complexity of the checks, you are indeed correct it is a
bit akward for the INT64_MAX if only llrint() is available
but with ff_rint64_clip() the following should work i think
if (d < INT_MIN || d > INT_MAX)
error
else
i = ff_rint64_clip(d) (or llrint() or others for this)
and
if (d < INT64_MIN || d > INT64_MAX)
error
else
i = ff_rint64_clip(d)
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
Rewriting code that is poorly written but fully understood is good.
Rewriting code that one doesnt understand is a sign that one is less smart
then the original author, trying to rewrite it will not make it better.
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