From: razorwarden-nobullshit at yahoo dot it
Operating system: Linux / win 2k
PHP version: 4.3.10
PHP Bug Type: Math related
Bug description: problem with floats...
Description:
------------
PHP seems to have problems with floats... infact -0.04 + 0.04 is not equal
to 1.3877787807814E-017... the operation $num = -0.04 + 0.04 itself returns
0 as expected but if we start from a bigger negative value (such as -4) and
we add for several times a positive value (0.04), the result may vary and
are quite weird. Note that this problem seems to vary from machine to
machine.
I've also tried the same code with c# and other languages and the output
is the expected one, so there's no doubt that this is really a php bug.
Reproduce code:
---------------
<?php
$start = -0.2;
$end = 0.2;
$step = 0.04;
for ($i = $start; $i <= $end; $i += $i) {
echo $i . "<br />\n";
}
?>
Expected result:
----------------
-0.2
-0.16
-0.12
-0.08
-0.04
0
0.04
0.08
0.12
0.16
0.2
Actual result:
--------------
-0.2
-0.16
-0.12
-0.08
-0.04
1.3877787807814E-017
0.04
0.08
0.12
0.16
note that there ISN'T the last number (0.2), most probably because the
float value is smt like 2.000000000000001
With $start = -8 and $end = 8, the middle output is:
[...]
-0.31999999999999
-0.27999999999999
-0.23999999999999
-0.19999999999999
-0.15999999999999
-0.11999999999999
-0.079999999999993
-0.039999999999993
6.5641936330962E-015
0.040000000000007
0.080000000000007
0.12000000000001
0.16000000000001
0.20000000000001
0.24000000000001
0.28000000000001
[...]
With my machine (win 2k, php 4.3.10), and
[...]
-0.08
-0.04
6.5641936330962E-015
0.04
0.08
[...]
on my web server (linux, php 4.3.10 with modifications, see the links
below for further details)
A page with this code is online at:
http://nemea.altervista.org/alfa/phpbug.php
Complete php info at: http://nemea.altervista.org/alfa/phpinfo.php
--
Edit bug report at http://bugs.php.net/?id=32003&edit=1
--
Try a CVS snapshot (php4): http://bugs.php.net/fix.php?id=32003&r=trysnapshot4
Try a CVS snapshot (php5.0):
http://bugs.php.net/fix.php?id=32003&r=trysnapshot50
Try a CVS snapshot (php5.1):
http://bugs.php.net/fix.php?id=32003&r=trysnapshot51
Fixed in CVS: http://bugs.php.net/fix.php?id=32003&r=fixedcvs
Fixed in release: http://bugs.php.net/fix.php?id=32003&r=alreadyfixed
Need backtrace: http://bugs.php.net/fix.php?id=32003&r=needtrace
Need Reproduce Script: http://bugs.php.net/fix.php?id=32003&r=needscript
Try newer version: http://bugs.php.net/fix.php?id=32003&r=oldversion
Not developer issue: http://bugs.php.net/fix.php?id=32003&r=support
Expected behavior: http://bugs.php.net/fix.php?id=32003&r=notwrong
Not enough info:
http://bugs.php.net/fix.php?id=32003&r=notenoughinfo
Submitted twice:
http://bugs.php.net/fix.php?id=32003&r=submittedtwice
register_globals: http://bugs.php.net/fix.php?id=32003&r=globals
PHP 3 support discontinued: http://bugs.php.net/fix.php?id=32003&r=php3
Daylight Savings: http://bugs.php.net/fix.php?id=32003&r=dst
IIS Stability: http://bugs.php.net/fix.php?id=32003&r=isapi
Install GNU Sed: http://bugs.php.net/fix.php?id=32003&r=gnused
Floating point limitations: http://bugs.php.net/fix.php?id=32003&r=float
No Zend Extensions: http://bugs.php.net/fix.php?id=32003&r=nozend
MySQL Configuration Error: http://bugs.php.net/fix.php?id=32003&r=mysqlcfg
