Doc #77778 [Csd]: 0.0 is falsy but docs do not say -0.0 is falsy too

Edit report at https://bugs.php.net/bug.php?id=77778&edit=1 ID: 77778 User updated by: lewisje at alumni dot iu dot edu Reported by: lewisje at alumni dot iu dot edu Summary: 0.0 is falsy but docs do not say -0.0 is falsy too Status: Closed Type: Documentation Problem Package: *General Issues Operating System: CentOS 6 PHP Version: Irrelevant Assigned To: salathe Block user comment: N Private report: N New Comment: I just saw the new documentation page, and I should mention that there is no distinction between -0 and 0 for *integer* arithmetic, even though floating-point makes such a distinction: <?php var_dump(1/-0); // float(INF) var_dump(1/0); // float(INF) ?> Previous Comments: ------------------------------------------------------------------------ [2019-03-21 19:30:46] salathe@php.net Automatic comment on behalf of salathe Revision: http://git.php.net/?p=doc/en.git;a=commit;h=096a3dce5d92652947579249761728eb4e48cdde Log: negative zero is falsy (fix bug #77778) ------------------------------------------------------------------------ [2019-03-21 19:26:46] salathe@php.net This bug has been fixed in the documentation's XML sources. Since the online and downloadable versions of the documentation need some time to get updated, we would like to ask you to be a bit patient. Thank you for the report, and for helping us make our documentation better. ------------------------------------------------------------------------ [2019-03-21 19:26:17] salathe@php.net Automatic comment from SVN on behalf of salathe Revision: http://svn.php.net/viewvc/?view=revision&amp;revision=347033 Log: negative zero is falsy (fix bug #77778) ------------------------------------------------------------------------ [2019-03-21 19:06:11] requinix@php.net > Sections 7.2 and 6.3 together imply that it is by design that 1/0.0 is INF and 1/-0.0 is -INF. Right. They could have said $n/0.0 == $n/-0.0 == NAN or DIV or something but they chose the arguably more useful +INF/-INF. It also means that according to IEEE +0.0 and -0.0 are treated inconsistently: equal in one place, not equal in another. Anyways, PHP does not distinguish between +0.0 and -0.0 because the IEEE-ness of PHP's floats is besides the point. In fact there have been bugs where PHP produces an unexpected "-0.0" which were fixed so it was "0.0". And everyone agrees that +0.0 === -0.0 should be true. Which is why saying that (bool)-0.0 should be true doesn't make sense - it should be false, as it already is. Which brings this to a question of documentation: whether or not to state that yes, in fact, -0.0 is falsy too. But like I said, an easy enough edit. ------------------------------------------------------------------------ [2019-03-21 18:42:02] lewisje at alumni dot iu dot edu As I showed above, even though -0.0 and 0.0 show as equal under strict equality, they are distinct values, because 1/-0.0 and 1/0.0 are the respective distinct values -INF and INF; this is by design, to quote from Section 5.7 of ANSI/IEEE Std 754-1985: http://www.validlab.com/754R/web-2008/standards/754.pdf > Comparisons shall ignore the sign of zero (so +0 = –0). Sections 7.2 and 6.3 together imply that it is by design that 1/0.0 is INF and 1/-0.0 is -INF. --- It does seem like a nitpick, but it just stuck out to me after I had noticed a similar distinction in Ecmascript (Crockford and many other expositors don't make a distinction, while the Definitive Guide by Flanagan did make it); also, the way I mentioned earlier to be able to distinguish the positive and negative zero floats is exactly what is done in the polyfill for Object.is from ES6. (I'm not saying here that it's vital for PHP to have some built-in function that distinguishes -0.0 from 0.0 and compares NAN as equal to itself, the way Object.is does.) ------------------------------------------------------------------------ The remainder of the comments for this report are too long. To view the rest of the comments, please view the bug report online at https://bugs.php.net/bug.php?id=77778 -- Edit this bug report at https://bugs.php.net/bug.php?id=77778&edit=1