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

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