ID: 35656 User updated by: php at lipfi dot ch Reported By: php at lipfi dot ch Status: Bogus Bug Type: Scripting Engine problem Operating System: Gentoo Linux 2005.1 PHP Version: 5.1.1 New Comment:
I fear your decision to mark this as bogus was a very quick one. http://www.php.net/manual/en/language.operators.arithmetic.php does not tell me anywhere that the commutative law is not valid in PHP. Also note that I'm very well aware of floats having limited precision, but -0 is no defined value and certainly not something you'd expect to get as a result of a multiplication. And certainly not depending on the operands order. 0*0.02 = -0 0.02*0 = 0 where var_dump() certainly knows that -0 == 0, but the engines core seems not to. I certainly expect the arithmetics in PHP to work like it's supposed to. This means adhering to the commutative law which basically means that I can interchange the operands in a multiplication. Besides: -0 is IMHO not a valid value. It's either 0 or not 0, but not -0. I'd really appreciate a further comment of why the behaviour whitnessed here is really working as intended and where that is documented in the manual. Thank you Philip Previous Comments: ------------------------------------------------------------------------ [2005-12-13 11:02:53] [EMAIL PROTECTED] Thank you for taking the time to write to us, but this is not a bug. Please double-check the documentation available at http://www.php.net/manual/ and the instructions on how to report a bug at http://bugs.php.net/how-to-report.php ------------------------------------------------------------------------ [2005-12-13 11:00:33] php at lipfi dot ch Description: ------------ When multiplying two float values, one being 0, one being negative, it's possible to either get 0 or -0 (!) as a result depending on the operands order. This is IMHO not how math is supposed to work. Additionally, I'm seing discrepancies between the variables value and what var_dump() things it contains. The problem is very simple to reproduce Reproduce code: --------------- <?php $v = 0*-0.02; var_dump($v); echo "$v\n"; $v = floatval($v); echo "$v\n\n"; $v = -0.02*0; var_dump($v); echo "$v\n"; ?> Expected result: ---------------- float(0) 0 0 float(0) 0 Actual result: -------------- float(0) -0 -0 float(0) 0 (the -0 obviously being the problem here) ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/?id=35656&edit=1
