[FFmpeg-devel] [PATCH] avutil/rational: Document what is to be expected from av_d2q() of doubles representing rational numbers

[FFmpeg-devel] [PATCH] avutil/rational: Document what is to be expected from av_d2q() of doubles representing rational numbers

[Michael Niedermayer]

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
 libavutil/rational.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/libavutil/rational.h b/libavutil/rational.h
index 8cbfc8e0669..c6ac9fb1d91 100644
--- a/libavutil/rational.h
+++ b/libavutil/rational.h
@@ -168,6 +168,10 @@ static av_always_inline AVRational av_inv_q(AVRational q)
  * In case of infinity, the returned value is expressed as `{1, 0}` or
  * `{-1, 0}` depending on the sign.
  *
+ * In general rational numbers with |num| <= 1<<26 && |den| <= 1<<26
+ * can be recovered exactly from their double representation.
+ * (no exceptions where found within 100M random ones)
+ *
  * @param d   `double` to convert
  * @param max Maximum allowed numerator and denominator
  * @return `d` in AVRational form
-- 
2.17.1

_______________________________________________
ffmpeg-devel mailing list
ffmpeg-devel@ffmpeg.org
https://ffmpeg.org/mailman/listinfo/ffmpeg-devel

To unsubscribe, visit link above, or email
ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".

Re: [FFmpeg-devel] [PATCH] avutil/rational: Document what is to be expected from av_d2q() of doubles representing rational numbers

[epirat07]

On 31 Jan 2024, at 20:47, Michael Niedermayer wrote:

> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
>  libavutil/rational.h | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/libavutil/rational.h b/libavutil/rational.h
> index 8cbfc8e0669..c6ac9fb1d91 100644
> --- a/libavutil/rational.h
> +++ b/libavutil/rational.h
> @@ -168,6 +168,10 @@ static av_always_inline AVRational av_inv_q(AVRational q)
>   * In case of infinity, the returned value is expressed as `{1, 0}` or
>   * `{-1, 0}` depending on the sign.
>   *
> + * In general rational numbers with |num| <= 1<<26 && |den| <= 1<<26
> + * can be recovered exactly from their double representation.
> + * (no exceptions where found within 100M random ones)

I think you meant „were“ here instead of „where“?

> + *
>   * @param d   `double` to convert
>   * @param max Maximum allowed numerator and denominator
>   * @return `d` in AVRational form
> -- 
> 2.17.1
>
> _______________________________________________
> ffmpeg-devel mailing list
> ffmpeg-devel@ffmpeg.org
> https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>
> To unsubscribe, visit link above, or email
> ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".
_______________________________________________
ffmpeg-devel mailing list
ffmpeg-devel@ffmpeg.org
https://ffmpeg.org/mailman/listinfo/ffmpeg-devel

To unsubscribe, visit link above, or email
ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".

Re: [FFmpeg-devel] [PATCH] avutil/rational: Document what is to be expected from av_d2q() of doubles representing rational numbers

[Michael Niedermayer]

[-- Attachment #1.1: Type: text/plain, Size: 1452 bytes --]

On Wed, Jan 31, 2024 at 09:30:44PM +0100, epirat07@gmail.com wrote:
> 
> 
> On 31 Jan 2024, at 20:47, Michael Niedermayer wrote:
> 
> > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> > ---
> >  libavutil/rational.h | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/libavutil/rational.h b/libavutil/rational.h
> > index 8cbfc8e0669..c6ac9fb1d91 100644
> > --- a/libavutil/rational.h
> > +++ b/libavutil/rational.h
> > @@ -168,6 +168,10 @@ static av_always_inline AVRational av_inv_q(AVRational q)
> >   * In case of infinity, the returned value is expressed as `{1, 0}` or
> >   * `{-1, 0}` depending on the sign.
> >   *
> > + * In general rational numbers with |num| <= 1<<26 && |den| <= 1<<26
> > + * can be recovered exactly from their double representation.
> > + * (no exceptions where found within 100M random ones)
> 
> I think you meant „were“ here instead of „where“?

fixed
also tested 1B more cases
and 1<<27 as a limit btw fails as is to be expected fro the amount
of bits in the mantisse

thx

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Any man who breaks a law that conscience tells him is unjust and willingly 
accepts the penalty by staying in jail in order to arouse the conscience of 
the community on the injustice of the law is at that moment expressing the 
very highest respect for law. - Martin Luther King Jr

[-- Attachment #1.2: signature.asc --]
[-- Type: application/pgp-signature, Size: 195 bytes --]

[-- Attachment #2: Type: text/plain, Size: 251 bytes --]

_______________________________________________
ffmpeg-devel mailing list
ffmpeg-devel@ffmpeg.org
https://ffmpeg.org/mailman/listinfo/ffmpeg-devel

To unsubscribe, visit link above, or email
ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".