Re: [FFmpeg-devel] [PATCH 1/2] libavutil/eval: introduce UINT64_MAX constant

[Michael Niedermayer <michael@niedermayer.cc>]

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On Mon, Jan 01, 2024 at 08:38:58PM +0100, Stefano Sabatini wrote:
> This might be useful, e.g. when setting the random seed expressed as a
> uint64_t.
> ---
>  doc/utils.texi   | 3 +++
>  libavutil/eval.c | 1 +
>  2 files changed, 4 insertions(+)
> 
> diff --git a/doc/utils.texi b/doc/utils.texi
> index 0c4f146f4f..ac9b63826e 100644
> --- a/doc/utils.texi
> +++ b/doc/utils.texi
> @@ -1030,6 +1030,9 @@ area of the unit disc, approximately 3.14
>  exp(1) (Euler's number), approximately 2.718
>  @item PHI
>  golden ratio (1+sqrt(5))/2, approximately 1.618
> +@item UINT64_MAX
> +maximum value expressed as an unsigned integer, corresponds to

> +18446744073709551616 ((2^64)-1)

this doesnt look right
2^x is even
even -1 is odd
18446744073709551616 should be a odd number
18446744073709551615 looks more likely

double precission also doesnt like exactly ((2^64)-1) because the mantisse has too few bits

(U)INT64_MIN should work though exactly in double

thx

[...]
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Avoid a single point of failure, be that a person or equipment.

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