ID: 47418 Updated by: scott...@php.net Reported By: cu19 at gmx dot de Status: Bogus Bug Type: *Math Functions Operating System: WinXP SP3 PHP Version: 5.3CVS-2009-02-17 (CVS) New Comment:
sc...@skinny [~] $ php -r 'var_dump(number_format(3.9, 2));' string(4) "3.90" Can't reproduce this on Linux. Previous Comments: ------------------------------------------------------------------------ [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] scott...@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 ------------------------------------------------------------------------ [2009-02-17 09:45:57] cu19 at gmx dot de Description: ------------ In my script im using number_format to format values read from a MSSQL-DB via ODBC. Works fine, as long as the value is not equal to 1.9, 2.9, 3.9, 1.7 and probably some others. I've made the following test script: <?php echo number_format(3.9, 2); ?> Output is expected to be 3.90, but in fact is 9.8: I don't know where this colon does come from, but for me it seems to be an error in number_format. Using sprintf('%4.2f', 3.9) leads to the same problem. I'm using PHP 5.2.8 on Apache 2.2.9 on Windows XP MCE SP3. When Apache just got restarted, the test script works fine, but when executing my (quite large) script with several ODBC queries, it produces this error and after execution also the test script fails. I've tried using 5.3 snapshot and 5.2.8 snap, the error occurs also. With PHP 5.2.6, the error didn't occur as far as I can remember. The error doesn't occur, too, with CLI. Any idea? Or is it about the Apache webserver? Reproduce code: --------------- echo number_format(3.9, 2); Expected result: ---------------- 3.90 Actual result: -------------- 3.8: ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/?id=47418&edit=1
