From: hakon at haugnes dot name
Operating system: Redhat 8.0
PHP version: 4.3.2
PHP Bug Type: *Math Functions
Bug description: modulus operator problem with large numbers
Description:
------------
The modulus operator % returns wrong results if the number gets large. In
a program used to calculate primes, it will find that large numbers,
ending in 5, are prime. The following are calculations using % on such a
large number, note that all numbers used in the MOD calculation are whole
integers (and should not suffer rounding by MOD):
MOD: 53253252355 % 3=1
DIV: 53253252355 / 3=17751084118.333332061767578125
MOD: 53253252355 % 4=3
DIV: 53253252355 / 4=13313313088.75
MOD: 53253252355 % 5=2
DIV: 53253252355 / 5=10650650471
Obviously, any number ending in 5 cannot be prime, since it will always be
divisible by 5. The MOD result on 5 is therefore wrong, as the division
proves.
Reproduce code:
---------------
$i=53253252355;
ini_set("precision",35);
for ($m=2; $m<=$i; $m++){
echo "MOD: $i % $m=". $i % $m ;
echo "DIV: $i / $m=". $i/$m ."<Br>";
}
Expected result:
----------------
I would expect to see
MOD: 53253252355 % 3=1
DIV: 53253252355 / 3=17751084118.333332061767578125
MOD: 53253252355 % 4=3
DIV: 53253252355 / 4=13313313088.75
MOD: 53253252355 % 5=0
DIV: 53253252355 / 5=10650650471
Actual result:
--------------
However, this is produced: ([THE ERROR] added for your convenience)
MOD: 53253252355 % 3=1
DIV: 53253252355 / 3=17751084118.333332061767578125
MOD: 53253252355 % 4=3
DIV: 53253252355 / 4=13313313088.75
MOD: 53253252355 % 5=2 [THE ERROR]
DIV: 53253252355 / 5=10650650471
--
Edit bug report at http://bugs.php.net/?id=25328&edit=1
--
Try a CVS snapshot (php4): http://bugs.php.net/fix.php?id=25328&r=trysnapshot4
Try a CVS snapshot (php5): http://bugs.php.net/fix.php?id=25328&r=trysnapshot5
Fixed in CVS: http://bugs.php.net/fix.php?id=25328&r=fixedcvs
Fixed in release: http://bugs.php.net/fix.php?id=25328&r=alreadyfixed
Need backtrace: http://bugs.php.net/fix.php?id=25328&r=needtrace
Try newer version: http://bugs.php.net/fix.php?id=25328&r=oldversion
Not developer issue: http://bugs.php.net/fix.php?id=25328&r=support
Expected behavior: http://bugs.php.net/fix.php?id=25328&r=notwrong
Not enough info: http://bugs.php.net/fix.php?id=25328&r=notenoughinfo
Submitted twice: http://bugs.php.net/fix.php?id=25328&r=submittedtwice
register_globals: http://bugs.php.net/fix.php?id=25328&r=globals
PHP 3 support discontinued: http://bugs.php.net/fix.php?id=25328&r=php3
Daylight Savings: http://bugs.php.net/fix.php?id=25328&r=dst
IIS Stability: http://bugs.php.net/fix.php?id=25328&r=isapi
Install GNU Sed: http://bugs.php.net/fix.php?id=25328&r=gnused
