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Bug #10131 Round error
Submitted: 2001-04-03 03:46 UTC Modified: 2001-04-03 11:16 UTC
From: woprog at hotmail dot com Assigned:
Status: Not a bug Package: Math related
PHP Version: 4.0.4pl1 OS: Red Hat Linux 6.2
Private report: No CVE-ID: None
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From: woprog at hotmail dot com
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 [2001-04-03 03:46 UTC] woprog at hotmail dot com
Execute this script:
<?
	$a = 250.02;
	$b = 210.10;
	$c =  39.92;

	echo "a = $a<br>\n";
	echo "b = $b<br>\n";
	echo "c = $c<br>\n";

	echo "(b+c)-a = " . (($b+$c)-$a) . "<br>\n";
?>

It SHOULD echo:
a = 250.02
b = 210.1
c = 39.92
(b+c)-a = 0

But it echoes on my machine:
a = 250.02
b = 210.1
c = 39.92
(b+c)-a = -2.8421709430404E-14

When you change the values, for example like this:
<?
	$a = 250.022;
	$b = 210.101;
	$c =  39.921;
?>
it echoes the correct values... if against all odds I am doing something wrong, please tell me....!

Marc, a very happy php programmer!


P.S. I compiled PHP with this command line:

'./configure' '--with-mysql' '--with-pgsql' '--with-esoob' '--with-magic-quotes' '--with-apxs' '--with-ftp' '--with-config-file-path=.'

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 [2001-04-03 04:15 UTC] derick@php.net
This is not a bug in PHP. it's how floating point math works, and there is nothing that we can do to change it.
The problem is that these floating point number are stored as a as good as possible representation of the numbers you use, but it's not possible to get them stored exactly as you want them to be.
 
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