ID: 32003
User updated by: razorwarden-nobullshit at yahoo dot it
Reported By: razorwarden-nobullshit at yahoo dot it
-Status: Bogus
+Status: Open
Bug Type: Math related
Operating System: Linux / win 2k
PHP Version: 4.3.10
New Comment:
my question is... Why i have this problem with php ONLY?? It seems much
like this is a php problem to me, not a floating numbers problem. And
anyway, i can understand that if i do 2 / 3 i'll never have the exact
value, but an approximated one. But -0.04 + 0.04 =
0.000000000000000012644358?? lol that's not a floating point fault,
that's a php fault m8...
Previous Comments:
------------------------------------------------------------------------
[2005-02-16 20:44:27] [EMAIL PROTECTED]
Floating point values have a limited precision. Hence a value might
not have the same string representation after any processing. That also
includes writing a floating point value in your script and directly
printing it without any mathematical operations.
Thank you for your interest in PHP.
------------------------------------------------------------------------
[2005-02-16 19:35:54] razorwarden-nobullshit at yahoo dot it
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 this bug report at http://bugs.php.net/?id=32003&edit=1
