#49300 [Bgs]: very bizarre loops with decimal numbers

ID: 49300 Updated by: scottmac@php.net Reported By: looris at gmail dot com Status: Bogus Bug Type: Unknown/Other Function Operating System: debian stable PHP Version: 5.2.10 New Comment: Unfortunately you're not understanding how floating point maths is represented with a computer. Read the link that derick pointed you to or have a quick look at wikipedia. Previous Comments: ------------------------------------------------------------------------ [2009-08-20 10:36:22] looris at gmail dot com what are you talking about? string representation? the second loop loops 8 times, when it should have looped only 7 times. and using < or <= gives exactly the same result: it still loops for 0.8 when it shouldn't (since i wrote $value<0.8) I assumed you would notice it but clearly you didn't, I'll be more descriptive next time. We do agree that if $value is 0.8, the expression $value<0.8 is FALSE, now do we? ------------------------------------------------------------------------ [2009-08-20 08:58:58] derick@php.net Floating point values have a limited precision. Hence a value might not have the same string representation after any processing. That also includes writing a floating point value in your script and directly printing it without any mathematical operations. If you would like to know more about "floats" and what IEEE 754 is, read this: http://docs.sun.com/source/806-3568/ncg_goldberg.html Thank you for your interest in PHP. . ------------------------------------------------------------------------ [2009-08-19 20:39:01] looris at gmail dot com Description: ------------ Just look at the code. Reproduce code: --------------- <?php for ($value=0.1; $value<0.6; $value+=0.1) { echo $value."\n"; } echo "\n"; for ($value=0.1; $value<0.8; $value+=0.1) { echo $value."\n"; } ?> Expected result: ---------------- 0.1 0.2 0.3 0.4 0.5 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Actual result: -------------- 0.1 0.2 0.3 0.4 0.5 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/?id=49300&edit=1