Doc #77778 [Com]: 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 Comment 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: Open Type: Documentation Problem Package: *General Issues Operating System: CentOS 6 PHP Version: Irrelevant Block user comment: N Private report: N New Comment: 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.) Previous Comments: ------------------------------------------------------------------------ [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