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Date: Tue, 20 Dec 2022 18:14:04 +0900
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To: internals@lists.php.net
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Subject: Re: [PHP-DEV] ext-random: add random_float() ?
From: g-kudo@colopl.co.jp (Go Kudo)

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2022=E5=B9=B412=E6=9C=8820=E6=97=A5(=E7=81=AB) 17:15 Hans Henrik Bergan <di=
vinity76@gmail.com>:

> btw while we're on the topic, does anyone know if this function gives
> biased results/is-safe or not? i honestly don't know:
> function random_float(float $min, float $max): float
> {
>     if ($min > $max) throw new \InvalidArgumentException("min must be
> less than max");
>     if ($min =3D=3D=3D $max) return $min;
>     return $min + random_int(0, PHP_INT_MAX) / PHP_INT_MAX * ($max - $min=
);
> }
>
>
> On Tue, 20 Dec 2022 at 09:06, Hans Henrik Bergan <divinity76@gmail.com>
> wrote:
> >
> > >returns a value between 0.0 and 1.0.
> >
> > wouldn't it be better to follow random_int(int $min, int $max) design? =
eg
> > random_float(float $min, float $max): float
> >
> > On Tue, 20 Dec 2022 at 07:27, Go Kudo <g-kudo@colopl.co.jp> wrote:
> > >
> > > Hi Internals.
> > >
> > > Congratulations on the release of PHP 8.2.
> > > I just recently upgraded production PHP from 7.4 to 8.1 :)
> > >
> > > Now that my work is done, I was thinking about a proposal for a
> sunsetting
> > > of existing functions for PHP 8.3 based on the features introduced in
> > > ext-random, and I realized that there is no alternative to
> `lcg_value()`.
> > >
> > > Essentially, this could be completely replaced by
> > > Random\Randomizer::getFloat(), but there are easier `random_int()` an=
d
> > > `random_bytes()` functions for ints and strings.
> > >
> > > The Randomizer may be overkill and complicated for PHP use cases wher=
e
> > > random number reproducibility is not required in many cases.
> > >
> > > So, why not add a `random_float(): float` function? This function,
> like the
> > > others, uses CSPRNG and returns a value between 0.0 and 1.0. This
> behavior
> > > is `Closed` `Closed`.
> > >
> > > Opinions are welcome.
> > >
> > > Regards,
> > > Go Kudo
>

Hi.

The dangers of generating floating-point random numbers from PHP integer
values are explained in detail in Tim and Joshua's RFC.

https://wiki.php.net/rfc/randomizer_additions

I missed it at first too, and was negative about adding
`Randomizer::getFloat()` ...
In general, I think this problem is less noticeable and the absence of the
random_float() function increases the likelihood of incorrect
implementations in userland.

Regards,
Go Kudo

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