Bug #64928 [NEW]: Summing floats yields different result when order of summands is changed

From: thz at plista dot com Operating system: Ubuntu 12.04 PHP version: 5.5Git-2013-05-27 (Git) Package: Math related Bug Type: Bug Bug description:Summing floats yields different result when order of summands is changed Description: ------------ First of all: I am aware of how floats work and that they are only approximations of their ideal values. I found an inconsistency in how they are handled when added, please see the code below. Variable $a and $b are created by summing up three floats <1.0. The only difference is the order of the summands. Both variables should have exactly the same value, yet $a evaluates to 1.0 and $b to <1.0. Test script: --------------- <?php $a = array_sum(array(0.6, 0.3, 0.1)); $b = array_sum(array(0.1, 0.3, 0.6)); var_dump($a); // float(1) var_dump($b); // float(1) var_dump($a == $b); // bool(false) var_dump(intval($a)); // int(0) var_dump(intval($b)); // int(1) $c = $a - 1; var_dump($c); // float(-1.1102230246252E-16) Expected result: ---------------- float(1) float(1) bool(true) int(1) int(1) float(0) Actual result: -------------- float(1) float(1) bool(false) int(0) int(1) float(-1.1102230246252E-16) -- Edit bug report at https://bugs.php.net/bug.php?id=64928&edit=1 -- Try a snapshot (PHP 5.4): https://bugs.php.net/fix.php?id=64928&r=trysnapshot54 Try a snapshot (PHP 5.3): https://bugs.php.net/fix.php?id=64928&r=trysnapshot53 Try a snapshot (trunk): https://bugs.php.net/fix.php?id=64928&r=trysnapshottrunk Fixed in SVN: https://bugs.php.net/fix.php?id=64928&r=fixed Fixed in release: https://bugs.php.net/fix.php?id=64928&r=alreadyfixed Need backtrace: https://bugs.php.net/fix.php?id=64928&r=needtrace Need Reproduce Script: https://bugs.php.net/fix.php?id=64928&r=needscript Try newer version: https://bugs.php.net/fix.php?id=64928&r=oldversion Not developer issue: https://bugs.php.net/fix.php?id=64928&r=support Expected behavior: https://bugs.php.net/fix.php?id=64928&r=notwrong Not enough info: https://bugs.php.net/fix.php?id=64928&r=notenoughinfo Submitted twice: https://bugs.php.net/fix.php?id=64928&r=submittedtwice register_globals: https://bugs.php.net/fix.php?id=64928&r=globals PHP 4 support discontinued: https://bugs.php.net/fix.php?id=64928&r=php4 Daylight Savings: https://bugs.php.net/fix.php?id=64928&r=dst IIS Stability: https://bugs.php.net/fix.php?id=64928&r=isapi Install GNU Sed: https://bugs.php.net/fix.php?id=64928&r=gnused Floating point limitations: https://bugs.php.net/fix.php?id=64928&r=float No Zend Extensions: https://bugs.php.net/fix.php?id=64928&r=nozend MySQL Configuration Error: https://bugs.php.net/fix.php?id=64928&r=mysqlcfg