#49715 [NEW]: float to string conversions

From: terrafrost at gmail dot com Operating system: Windows XP PHP version: 5.2.11 PHP Bug Type: Scripting Engine problem Bug description: float to string conversions Description: ------------ Displaying a float in base-10 when fractional values are involved is difficult, as per <http://php.net/float>. Even if fractional values aren't involved, displaying the float might still be problematic, if the number you're trying to display is to big to be stored in the mantissa of a floating point number. Problem is, floating point numbers aren't always displayed correctly, even if the mantissa can hold the number in question. For example, if you have a double precision floating point number, your mantissa has 53 bits. The following corroborates this: <?php $test = 1; $bits = 0; while (fmod($test, 2) == 1) { $test = 2 * $test + 1; $bits++; } echo $bits; ?> That, for me, displays 53. The problem occurs with anything utilizing 48 or more mantissa bits: <?php $bits = 0; while (true) { if (bcpow(2, $bits) != (string) pow(2, $bits)) { break; } $bits++; } echo $bits; ?> Reproduce code: --------------- <?php echo pow(2, 52); echo "\r\n"; echo 4503599627370496; echo "\r\n"; echo pow(2, 52) == 4503599627370496 ? 'equal' : 'not equal'; echo "\r\n"; echo pow(2, 52) == 4503599627370500 ? 'equal' : 'not equal'; ?> Expected result: ---------------- 4503599627370496 4503599627370496 equal not equal Actual result: -------------- 4503599627370500 4503599627370500 equal not equal -- Edit bug report at http://bugs.php.net/?id=49715&edit=1 -- Try a snapshot (PHP 5.2): http://bugs.php.net/fix.php?id=49715&r=trysnapshot52 Try a snapshot (PHP 5.3): http://bugs.php.net/fix.php?id=49715&r=trysnapshot53 Try a snapshot (PHP 6.0): http://bugs.php.net/fix.php?id=49715&r=trysnapshot60 Fixed in SVN: http://bugs.php.net/fix.php?id=49715&r=fixed Fixed in SVN and need be documented: http://bugs.php.net/fix.php?id=49715&r=needdocs Fixed in release: http://bugs.php.net/fix.php?id=49715&r=alreadyfixed Need backtrace: http://bugs.php.net/fix.php?id=49715&r=needtrace Need Reproduce Script: http://bugs.php.net/fix.php?id=49715&r=needscript Try newer version: http://bugs.php.net/fix.php?id=49715&r=oldversion Not developer issue: http://bugs.php.net/fix.php?id=49715&r=support Expected behavior: http://bugs.php.net/fix.php?id=49715&r=notwrong Not enough info: http://bugs.php.net/fix.php?id=49715&r=notenoughinfo Submitted twice: http://bugs.php.net/fix.php?id=49715&r=submittedtwice register_globals: http://bugs.php.net/fix.php?id=49715&r=globals PHP 4 support discontinued: http://bugs.php.net/fix.php?id=49715&r=php4 Daylight Savings: http://bugs.php.net/fix.php?id=49715&r=dst IIS Stability: http://bugs.php.net/fix.php?id=49715&r=isapi Install GNU Sed: http://bugs.php.net/fix.php?id=49715&r=gnused Floating point limitations: http://bugs.php.net/fix.php?id=49715&r=float No Zend Extensions: http://bugs.php.net/fix.php?id=49715&r=nozend MySQL Configuration Error: http://bugs.php.net/fix.php?id=49715&r=mysqlcfg