Bug #52355 [Opn->Csd]: Negating zero does not produce negative zero

Edit report at https://bugs.php.net/bug.php?id=52355&edit=1 ID: 52355 Updated by: ajf@php.net Reported by: spoon dot reloaded at gmail dot com Summary: Negating zero does not produce negative zero -Status: Open +Status: Closed Type: Bug Package: Math related PHP Version: 5.3.2 Block user comment: N Private report: N New Comment: Automatic comment on behalf of ajf@ajf.me Revision: http://git.php.net/?p=php-src.git;a=commit;h=a4648ded430985e019b446939c4ff5bef36c0b91 Log: Fix bug #52355 Previous Comments: ------------------------------------------------------------------------ [2015-12-17 22:26:28] ajf@php.net This is a bug, marking as such. Still exists in PHP 7, annoyingly. ------------------------------------------------------------------------ [2013-06-26 15:51:06] dlsniper@php.net I've found that this break was introduced in 5.2.3, http://3v4l.org/MFa5s I'll try and investigate further. ------------------------------------------------------------------------ [2012-02-13 08:31:50] salsi at icosaedro dot it The zero negative could appear also in the simplest expressions, yielding quite unexpected results, as in $zn = -1 * 0.0; echo $zn; ==> -0 Under PHP several int expressions might result in a float value, and most programmers are unaware that their "exact" calculations are made in the quite obscure domain of the approximated floating-point numbers, possibly with safety and security related issues. Since $zn==0.0 and $zn===0.0 are both true, the only way I have found to detect the zero negative value is by comparing its representation as a string: if( $f === 0.0 and "$f" === "-0" ) echo "WARNING: it's zero negative!"; ------------------------------------------------------------------------ [2010-07-16 08:34:29] spoon dot reloaded at gmail dot com Nor can you specify -0 as a float literal: var_dump(-0.); float(0) ------------------------------------------------------------------------ [2010-07-16 08:31:54] spoon dot reloaded at gmail dot com Description: ------------ Using the unary negation operator on a float 0 (positive zero) value, simply returns positive zero again, instead of -0 (negative zero), like it does in other languages. var_dump(-(0.)); float(0) The negative zero exists and can be displayed properly, so that is not the problem: var_dump(-1/INF); float(-0) But for some reason there is no easy way to access it. Test script: --------------- var_dump(-(0.)); var_dump(-1/INF); Expected result: ---------------- float(-0) float(-0) Actual result: -------------- float(0) float(-0) ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=52355&edit=1