Edit report at http://bugs.php.net/bug.php?id=34427&edit=1
ID: 34427
Updated by: rasmus@php.net
Reported by: lukasz at knasiecki dot com
Summary: round function bug
Status: Bogus
Type: Bug
Package: Math related
Operating System: Windows XP
PHP Version: 5.0.5
New Comment:
From your original report 8.155 can't actually be represented accurately
internally in IEEE-754. It is actually stored as 8.15499999999999 so
when you
round that to 2 decimal places you are going to end up with 8.15.
Previous Comments:
------------------------------------------------------------------------
[2010-03-12 04:01:15] sonicpr at bol dot com dot br
<?php
function myround($n,$p=0) {
$div = pow(10,$p);
$sign = ($n > 0) ? +0.5 : -0.5;
return floor(0.000000000001 + ($sign + $div * $n))/$div;
}
echo round(9.5), ' => ', myround(9.5), chr(10); // 10 => 10
echo round(9.95,1), ' => ', myround(9.95,1), chr(10); // 10 => 10
echo round(9.995,2), ' => ', myround(9.995,2), chr(10); // 9.99 => 10
echo round(9.9995,3), ' => ', myround(9.9995,3), chr(10); // 10 => 10
echo round(9.99995,4), ' => ', myround(9.99995,4), chr(10); // 10 => 10
echo round(-9.5), ' => ', myround(-9.5), chr(10); // -10 => -10
echo round(-9.95,1), ' => ', myround(-9.95,1), chr(10); // -10 => -10
echo round(-9.995,2), ' => ', myround(-9.995,2), chr(10); // -9.99 =>
-10
echo round(-9.9995,3), ' => ', myround(-9.9995,3), chr(10); // -10 =>
-10
echo round(-9.99995,4), ' => ', myround(-9.99995,4), chr(10); // -10 =>
-10
echo round(8.155, 2), ' => ', myround(8.155, 2), chr(10); // 8.155 =>
8.16
/*
PHP 5.2.6-1+lenny6 with Suhosin-Patch 0.9.6.2 (cli) (built: Feb 9 2010
03:05:13)
Copyright (c) 1997-2008 The PHP Group
*/
?>
------------------------------------------------------------------------
[2005-09-08 14:45:57] lukasz at knasiecki dot com
Still, I am sure this is a bug. No software I use (Excel, Shopping
program) produces such results, like PHP
echo '<br>'.round(0.155*1, 2); >> gives 0,16
echo '<br>'.round(8.155*1, 2); >> gives 8,15
------------------------------------------------------------------------
[2005-09-08 14:32:09] tony2001@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.
------------------------------------------------------------------------
[2005-09-08 14:24:56] lukasz at knasiecki dot com
Description:
------------
Round function works with errors.
Reproduce code:
---------------
echo '<br>'.round(8.055, 2);
echo '<br>'.round(8.155, 2);
echo '<br>'.round(8.255, 2);
Expected result:
----------------
echo '<br>'.round(8.055, 2); //gives 8.06
echo '<br>'.round(8.155, 2); //gives 8.16
echo '<br>'.round(8.255, 2); //gives 8.26
Actual result:
--------------
echo '<br>'.round(8.055, 2); //gives 8.06
echo '<br>'.round(8.155, 2); //gives 8.15 !!!
echo '<br>'.round(8.255, 2); //gives 8.26
------------------------------------------------------------------------
--
Edit this bug report at http://bugs.php.net/bug.php?id=34427&edit=1