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To: Tim =?ISO-8859-1?Q?D=FCsterhus?= <tim@bastelstu.be>, PHP Internals List
	 <internals@lists.php.net>
Date: Sun, 31 Jul 2022 23:52:08 +0300
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Subject: Re: [PHP-DEV] Negative values in PcgOneseq128XslRr64::jump($advance)
From: sandfox@sandfox.me (Anton Smirnov)

On Sun, 2022-07-31 at 19:52 +0200, Tim D=C3=BCsterhus wrote:
> Hi
>=20
> On 7/31/22 17:50, Anton Smirnov wrote:
> > I'm writing a polyfill for ext-random and I noticed a small
> > weirdness.
> > PcgOneseq128XslRr64::jump() accepts negative $advance where it
> > automagically becomes unsigned positive.
>=20
> Yes, this is what happens when casting a negative signed integer to
> an=20
> unsigned integer. It will wrap around to the maximum positive number=20
> minus whatever the negative value was.
>=20
> > Does it make sense or maybe it's better to throw a ValueError
> > there?
>=20
> No it doesn't, especially since:
>=20
> $a =3D $pcg->generate();
> $pcg->jump(-1); // jumps back 2^64 - 1 steps in a 64-bit system
> var_dump($pcg->generate() =3D=3D=3D $a); // bool(false)
>=20
> The PCG state is 128 Bits, so a negative jump does not work as
> expected=20
> and thus should throw.
>=20
> Would you mind filing an issue in the tracker, so that it can be=20
> properly referenced (and thus you properly credited for this find)?
>=20
> https://github.com/php/php-src/issues
>=20
> Best regards
> Tim D=C3=BCsterhus

Done,=20
The issue: https://github.com/php/php-src/issues/9212
Proposed patch: https://github.com/php/php-src/pull/9213