Doc #77778 [Opn]: 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 Updated by: salathe@php.net 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: Open Type: Documentation Problem Package: *General Issues Operating System: CentOS 6 PHP Version: Irrelevant Block user comment: N Private report: N New Comment: 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. Previous Comments: ------------------------------------------------------------------------ [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.) ------------------------------------------------------------------------ [2019-03-21 18:14:05] requinix@php.net If 0.0 and -0.0 are strictly identical then under what logic should (bool)0.0 be false and (bool)-0.0 be true? Seems silly to me that the docs should have to point out that both 0.0 and -0.0 are false, but I suppose it's an easy enough edit that it's not worth arguing about. ------------------------------------------------------------------------ [2019-03-21 16:55:31] lewisje at alumni dot iu dot edu Description: ------------ --- From manual page: https://php.net/language.types.boolean --- Among the values listed as falsy is "the float 0.0 (zero)", but the float -0.0 is not listed; however, it is both falsy and distinct from 0.0: As ought to be pointed out in https://php.net/language.types.float, IEEE-754 floating-point arithmetic includes distinct 0.0 and -0.0 values; even though they will be treated as equal under strict equality, 1/0.0 is INF, while 1/-0.0 is -INF, again as in the IEEE-754 specification. Test script: --------------- <?php var_dump(1/0.0); // float(INF) var_dump(1/-0.0); // float(-INF) var_dump(-0.0 === 0.0); // bool(true) var_dump((bool)-0.0); // bool(false) ?> Expected result: ---------------- Based on the literal documentation, (bool)-0.0 ought to be true. Actual result: -------------- (bool)-0.0 is false, and as the other statements show, -0.0 can be distinguished from 0.0, which means that it is another falsy value. ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=77778&edit=1