Re: Negative values in PcgOneseq128XslRr64::jump($advance)

On Sun, 2022-07-31 at 19:52 +0200, Tim Düsterhus wrote: > Hi > > 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. > > Yes, this is what happens when casting a negative signed integer to > an > unsigned integer. It will wrap around to the maximum positive number > minus whatever the negative value was. > > > Does it make sense or maybe it's better to throw a ValueError > > there? > > No it doesn't, especially since: > > $a = $pcg->generate(); > $pcg->jump(-1); // jumps back 2^64 - 1 steps in a 64-bit system > var_dump($pcg->generate() === $a); // bool(false) > > The PCG state is 128 Bits, so a negative jump does not work as > expected > and thus should throw. > > Would you mind filing an issue in the tracker, so that it can be > properly referenced (and thus you properly credited for this find)? > > https://github.com/php/php-src/issues > > Best regards > Tim Düsterhus Done, The issue: https://github.com/php/php-src/issues/9212 Proposed patch: https://github.com/php/php-src/pull/9213