#41213 [NEW]: Subtracting 2 floats returns incorrect results

From: jsbruns at selectionsheet dot com Operating system: Windows NT Server PHP version: 5.2.1 PHP Bug Type: Math related Bug description: Subtracting 2 floats returns incorrect results Description: ------------ Attempting to subtract one floating point number from another returns the incorrect result. Float 1 is assigned in the code, float 2 is retrieved from a mysql DB field, which is of type DECIMAL(5,4). When subtracting $float1 from $float2 the result is: -7.105427357601E-015 Reproduce code: --------------- //Field discount2 is defined as type DECIMAL(5.4). Original value in database is 0.56, use PHP to multiply by 100 to get a whole number (56). $result = mysql_query("SELECT discount2 FROM product_discounts WHERE product_id = 'prod1'"); $discount2 = mysql_result($result)*100; $discount1 = 56; echo $discount1; //56 echo $discount2; //56 if ($discount2 != $discount1) echo "Discount1 not equal to Discount2"; //Y if (bccomp($discount1,$discount2) == 0) echo "Discount1 equal to Discount2"; //Y echo ($discount1 + $discount2); //112 echo ($discount1 - $discount2); //-7.105427357601E-015 Expected result: ---------------- When subtracting $discount1 from $discount2 I expected to get 0. When adding the two I get the expected 112. Actual result: -------------- When subtracting $discount1 from $discount2 I get: -7.105427357601E-015 -- Edit bug report at http://bugs.php.net/?id=41213&edit=1 -- Try a CVS snapshot (PHP 4.4): http://bugs.php.net/fix.php?id=41213&r=trysnapshot44 Try a CVS snapshot (PHP 5.2): http://bugs.php.net/fix.php?id=41213&r=trysnapshot52 Try a CVS snapshot (PHP 6.0): http://bugs.php.net/fix.php?id=41213&r=trysnapshot60 Fixed in CVS: http://bugs.php.net/fix.php?id=41213&r=fixedcvs Fixed in release: http://bugs.php.net/fix.php?id=41213&r=alreadyfixed Need backtrace: http://bugs.php.net/fix.php?id=41213&r=needtrace Need Reproduce Script: http://bugs.php.net/fix.php?id=41213&r=needscript Try newer version: http://bugs.php.net/fix.php?id=41213&r=oldversion Not developer issue: http://bugs.php.net/fix.php?id=41213&r=support Expected behavior: http://bugs.php.net/fix.php?id=41213&r=notwrong Not enough info: http://bugs.php.net/fix.php?id=41213&r=notenoughinfo Submitted twice: http://bugs.php.net/fix.php?id=41213&r=submittedtwice register_globals: http://bugs.php.net/fix.php?id=41213&r=globals PHP 3 support discontinued: http://bugs.php.net/fix.php?id=41213&r=php3 Daylight Savings: http://bugs.php.net/fix.php?id=41213&r=dst IIS Stability: http://bugs.php.net/fix.php?id=41213&r=isapi Install GNU Sed: http://bugs.php.net/fix.php?id=41213&r=gnused Floating point limitations: http://bugs.php.net/fix.php?id=41213&r=float No Zend Extensions: http://bugs.php.net/fix.php?id=41213&r=nozend MySQL Configuration Error: http://bugs.php.net/fix.php?id=41213&r=mysqlcfg