#47418 [Bgs->Fbk]: number_format misbehaving with some values

ID: 47418 Updated by: scottmac@php.net Reported By: cu19 at gmx dot de -Status: Bogus +Status: Feedback Bug Type: *Math Functions Operating System: WinXP SP3 PHP Version: 5.3CVS-2009-02-17 (CVS) Previous Comments: ------------------------------------------------------------------------ [2009-02-17 11:20:31] scottmac@php.net scott@skinny [~] $ php -r 'var_dump(number_format(3.9, 2));' string(4) "3.90" Can't reproduce this on Linux. ------------------------------------------------------------------------ [2009-02-17 10:35:08] cu19 at gmx dot de I don't think it's a problem with limited precision but rather about the function itself. I think a float should be able to represent 3 digits without a problem. The hex representation of the float that is to be formatted is 0x40799998, which equals to about 3.8999996. I think number_format should be able to round this to '3.90' instead of displaying it as '3.8:' ------------------------------------------------------------------------ [2009-02-17 10:18:32] scottmac@php.net Floating point values have a limited precision. Hence a value might not have the same string representation after any processing. That also includes writing a floating point value in your script and directly printing it without any mathematical operations. If you would like to know more about "floats" and what IEEE 754 is, read this: http://docs.sun.com/source/806-3568/ncg_goldberg.html Thank you for your interest in PHP. It's the way floating point numbers work in computers, the canned response gives you a link to read about this some more. ------------------------------------------------------------------------ [2009-02-17 10:13:49] cu19 at gmx dot de After some additional recherche, it seems to me that the value is first internally represented as '3.89'. Then, the function checks the truncated digit which is larger than 5. So the last digit in the result is increased by one. In ASCII, after the '9' comes the ':', so when the last char of '3.89' is increased by one, it becomes '3.8:'. So when increasing the last digit there must be checked if it's smaller than 9. What I don't understand is why it only occurs sometimes... Don't know the PHP sources and where to look for this, so I kindly ask someone to look after this function. ------------------------------------------------------------------------ [2009-02-17 09:48:15] cu19 at gmx dot de In fact the result is 3.8: 9.8: was a typo ------------------------------------------------------------------------ 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/47418 -- Edit this bug report at http://bugs.php.net/?id=47418&edit=1