#45978 [Opn->Bgs]: round() errors.

ID: 45978 Updated by: mattwil@php.net Reported By: firealwaysworks at gmail dot com -Status: Open +Status: Bogus Bug Type: Math related Operating System: Linux PHP Version: 5.2.6 New Comment: 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. The result of 21.33*1.015 is stored as slightly less than 21.64995 (21.649949999999997 on my Windows system), different than when you write the literal static value. The result of 21.33*1.015 when printing it (happens differently than round() function, so results may vary) or rounding 5-14 decimal places, those extra internal 9s are "rolled over." Previous Comments: ------------------------------------------------------------------------ [2008-09-03 02:09:39] firealwaysworks at gmail dot com Description: ------------ In this example the multiplication of two floats yields a number with 5 significant figures. The round() function incorrectly handles this number only when it is working with the answer to a mathematical operation. It is important to note that the round() function is working properly for static values. I found this because I am writing financial software in PHP. I have absolutely no doubt that this bug would cause our company to loose money. Reproduce code: --------------- print 21.33*1.015."<br>"; print round(21.33*1.015,2)."<br>"; print round(21.33*1.015,4)."<br>"; print round(21.64995,4); Expected result: ---------------- 21.64995 21.65 21.65 21.65 Actual result: -------------- 21.64995 21.65 21.6499 21.65 ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/?id=45978&edit=1