ID: 49871
Updated by: [email protected]
Reported By: daniel dot buschke at nextiraone dot de
Status: Bogus
Bug Type: Math related
Operating System: Linux
PHP Version: 5.2.11
New Comment:
Add
ini_set('precision',20);
to the top of your script. That sets the output precision and will
cause your var_dump() to show:
--------- 2.3199999999999998401 --------
float(2.3199999999999998401)
float(231.99999999999997158)
int(231)
--------- 8.2799999999999993605 --------
float(8.2799999999999993605)
float(827.99999999999988631)
int(827)
This precision setting, because it is lossy, isn't applied until you
try to convert the float to a string, usually on output, but as the
previous comment mentioned, you could force it to apply before output
with an explicit conversion. Or you can set your own fuzz factor and
use that. If we magically applied this precision setting on every math
operation, these small floating point errors would become much bigger
when you actually were expecting your floating point to behave as
floating point values.
Previous Comments:
------------------------------------------------------------------------
[2009-10-14 11:37:44] daniel dot buschke at nextiraone dot de
(int)(string)$b
that does the job but is ugly, too
------------------------------------------------------------------------
[2009-10-14 11:16:23] [email protected]
Floating point values have a limited precision. Hence a value might
not have the same string representation after any processing. That also
includes writing a floating point value in your script and directly
printing it without any mathematical operations.
If you would like to know more about "floats" and what IEEE
754 is, read this:
http://docs.sun.com/source/806-3568/ncg_goldberg.html
Thank you for your interest in PHP.
------------------------------------------------------------------------
[2009-10-14 08:36:03] daniel dot buschke at nextiraone dot de
Description:
------------
Hi,
when I convert following float:
float(232)
into an int I get:
int(231).
The float was calculated by 2.32 * 100. I know that this may result in
232.00000000001 or 231.999999999 but the behavior is unexcpected because
var_dump does not show the real (more or less wrong) float number.
This one is exact the same as #2835 but the bug was closed without any
further comments. The provided solution is unacceptable.
How to convert 2.32 into an integer of the value 232?
BTW: Please do not set this bug to bogus or closed with the default
text for that problem ;-). As you can see in your bugtracker the
community wants a solution for that. Please also remember that PHP is a
scripting language which mainly ignores datatypes. This problem is not
comprehensible to beginners (webdesigners ;-) ).
I do not want to blame you with that but I just want to find a usefull
solution. Please keep communication with community.
regards
Daniel
Reproduce code:
---------------
<?php
messUpFloat(2.32);
messUpFloat(8.28);
function messUpFloat($float) {
echo '--------- ' . $float . ' --------' . PHP_EOL;
$a = $float;
var_dump($a);
$b = $a * 100 + 0;
var_dump($b);
$c = (int)$b;
var_dump($c);
}
?>
Expected result:
----------------
--------- 2.32 --------
float(2.32)
float(232)
int(232)
--------- 8.28 --------
float(8.28)
float(828)
int(828)
or (but not preferred ;-) )
--------- 2.32 --------
float(2.32)
float(231.999999999999999)
int(231)
--------- 8.28 --------
float(8.28)
float(827.999999999999999)
int(827)
Actual result:
--------------
--------- 2.32 --------
float(2.32)
float(232)
int(231)
--------- 8.28 --------
float(8.28)
float(828)
int(827)
------------------------------------------------------------------------
--
Edit this bug report at http://bugs.php.net/?id=49871&edit=1
