#38321 [Opn->Bgs]: Oddness and errors with float precision

ID: 38321 Updated by: tony2001@php.net Reported By: ibexris at gmail dot com -Status: Open +Status: Bogus Bug Type: Unknown/Other Function Operating System: Fedora Core PHP Version: 5.1.4 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. Previous Comments: ------------------------------------------------------------------------ [2006-08-04 00:35:06] ibexris at gmail dot com Description: ------------ I just got bitten by a float precision problem and ceil() that affects several versions of php and definitely doesn't behave in a consistent manner. I've tested this on linux (x86 and x86_64) and OSX with the same results, so I don't believe that it's dependent on the system libraries. You'll also notice that the problem goes away by rounding the results below PHP's 14 digit float precision, and that it only affects certain numbers (which made this rather hard to track down). Reproduce code: --------------- <?php $x = 1.2 * 100; echo "$x\n", ceil($x), "\n"; $x = 1.1 * 100; echo "$x\n", ceil($x), "\n", ceil(round($x, 13)), "\n", ceil(round($x, 14)), "\n"; ?> Expected result: ---------------- 120 120 110 110 110 110 Actual result: -------------- 120 120 110 111 110 111 ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/?id=38321&edit=1