#37642 [Opn->Bgs]: 3 * 1.35 - 4.05 = 8.881784197E-16 but should be 0.0 (zero) (ALL versions!)

ID: 37642 Updated by: tony2001@php.net Reported By: richard at besite dot nl -Status: Open +Status: Bogus Bug Type: Scripting Engine problem Operating System: Linux and Windows XP 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: ------------------------------------------------------------------------ [2006-05-30 09:41:45] richard at besite dot nl Description: ------------ The calculation of this simple piece goes wrong: 3 * 1.35 - 4.05 Under Linux it gives: 8.881784197E-16 Under Windows it gives: 8.8817841970013E-016 Tested under Linux with: PHP4 4.4.2-1+b1 (Debian package php4 4.4.2-1), PHP5 5.1.2-1+b1 (Debian package php5 5.1.2-1), PHP5 5.1.2 (Ubutu package php5 5.1.2-ubuntu3). Tested under Windows with: PHP4 4.4.2, PHP5 5.1.4, PHP5 snapshot (5.2.0-dev of 05/30/2006), PHP6 snapshot (6.0.0 dev of 05/30/2006 8:30). Btw, "3 * 1.36 - 4.08 == 0" returns true like you would expect. Reproduce code: --------------- <?php var_dump( 3 * 1.35 - 4.05 == 0 ); print( 3 * 1.35 - 4.05 ); ?> Expected result: ---------------- bool(true) 0 Actual result: -------------- bool(false) 8.881784197E-16 ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/?id=37642&edit=1