Edit report at http://bugs.php.net/bug.php?id=51396&edit=1
ID: 51396 Comment by: codeslinger at compsalot dot com Reported by: codeslinger at compsalot dot com Summary: Math is Unreliable Status: Feedback Type: Bug Package: Math related Operating System: any PHP Version: Irrelevant New Comment: One further note, in the repro above, it has to be exactly 16 nines. by adding or removing a 9, it does not fail. Also, as far as I know, all of the failures have been on 32bit Intel cpu's. This probably will not fail on a 64bit cpu. Previous Comments: ------------------------------------------------------------------------ [2010-03-27 12:22:12] codeslinger at compsalot dot com well, it's hard to prove a negative. but I have run a bunch of tests on the Linux snapshot and it appears to be working fine. A VERY BIG THANKYOU I did not find any windows snapshots, the latest is 5.2.13 from Feb 24. based on the symptoms, my initial assumption was that this was caused by some kind of array corruption, this turned out to be wrong. the actual repro can be boiled down to one line... :-) echo (string) (double) -0.09999999999999999; With the caveat that there are other values which also trigger this. ------------------------------------------------------------------------ [2010-03-26 21:37:12] paj...@php.net Please try using this snapshot: http://snaps.php.net/php5.2-latest.tar.gz For Windows: http://windows.php.net/snapshots/ ------------------------------------------------------------------------ [2010-03-26 21:32:51] codeslinger at compsalot dot com as far as the low incidence of occurrence and the millions of users not seeing it. I've said all along that it is hard to reproduce. But when dealing with financial transactions, that is not good enough, it only takes one mistake to have a huge problem on your hands. Out of all of those millions of users, I'd venture to say that the very overwhelming majority are using php for string processing not number crunching. And in many cases where it does show up such as positioning something on a web page, it would be easy to shrug off. So there is no way to know how often this happens in the wild, based on user feedback. ------------------------------------------------------------------------ [2010-03-26 21:02:47] codeslinger at compsalot dot com The billing program was failing on multiple computers at multiple locations, it failed on XP and Windows 2000 with various cpus. Those were customer sites! I reproduced the problem on a vmware setup with windows 2000. This snowflake program is failing on Ubuntu Hardy 8.0.4 with all of the updates. This is the stock php that comes with Ubuntu. This is a Pentium M 32bit Laptop. I've never experienced a memory error on this computer and the fact of it's consistency would argue against this being some kind of hardware issue. Here is what I get when I run the simplefail in the default config. php -v PHP 5.2.4-2ubuntu5.10 with Suhosin-Patch 0.9.6.2 (cli) (built: Jan 6 2010 22:01:14) Copyright (c) 1997-2007 The PHP Group Zend Engine v2.2.0, Copyright (c) 1998-2007 Zend Technologies with Xdebug v2.0.3, Copyright (c) 2002-2007, by Derick Rethans with Zend Debugger v5.2.15, Copyright (c) 1999-2008, by Zend Technologies ========== php simplefail.php Selected onepair.txt, Found 1 items (string)(double) -0.1 === -0.1 which of course is correct But when we convert the value in an array it fails Conversion Error: PHP Math idx = 0 || '-0.1' !== '-0.0:' ===== THANK YOU I REALLY APPRECIATE THE HELP ------------------------------------------------------------------------ [2010-03-26 17:25:40] ahar...@php.net Well, it is the next character after '9', and the character string is built up in zend_dtoa() by adding a value L (presumably intended to be in the range 0..9) to '0'. If L somehow ends up being 10, you'd get a colon. With the values that are apparently causing problems (the problematic value in onepair.txt is 0.09999999999999999167...), it does kind of look like a rounding issue to me, although I've no idea why it's not being triggered by more than two or three users in that case. ------------------------------------------------------------------------ The remainder of the comments for this report are too long. To view the rest of the comments, please view the bug report online at http://bugs.php.net/bug.php?id=51396 -- Edit this bug report at http://bugs.php.net/bug.php?id=51396&edit=1
