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.

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.

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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.)

> 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.

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.

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)
?>

Thanks for mentioning it, but to what end: do you want the -0 example removed?

Yes, because there is not an integer -0 that is distinct from the integer 0; also, I don't know whether this is out of scope for the bug, but https://php.net/function.empty does not mention that the float -0.0 is treated as empty, even though it is:

<?php
var_dump(-0.0); // bool(true)
?>

Sorry, that code example was supposed to be this:

<?php
var_dump(empty(-0.0)); // bool(true)
?>