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Bug #46566 wrong calculating
Submitted: 2008-11-13 13:36 UTC Modified: 2008-11-13 13:39 UTC
From: krumb at valentins dot de Assigned:
Status: Not a bug Package: Math related
PHP Version: 5.2.6 OS: Suse Linux
Private report: No CVE-ID: None
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From: krumb at valentins dot de
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 [2008-11-13 13:36 UTC] krumb at valentins dot de 
Description:
------------
Some strange calculating mistake
It seems to happen in the second line at 7/100*100, echos zero, had to be zero but internal it seems thats not zero

Reproduce code:
---------------
<?

$share=100;
$discount=7/100*$share;
$brutto=5.8824/100*(100+19);
$brutto=round($brutto,2);
echo $brutto."-".$discount."=";
$new=$brutto-$discount;
echo $new;

?>

Expected result:
----------------
7-7=0

Actual result:
--------------
7-7=-8.881784197E-16

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 [2008-11-13 13:39 UTC] pajoye@php.net 
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.

.
 [2011-07-18 16:07 UTC] beno9119 at gmail dot com 
<?

$share=100;
$discount=7/100*$share;
$brutto=5.8824/100*(100+19);
$brutto=round($brutto,2);
echo $brutto."-".$discount."=";
$new=$brutto-$discount;
echo round($new,2);

?>
 
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