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Bug #52892 Casting/rounding problem
Submitted: 2010-09-20 13:25 UTC Modified: 2010-09-20 17:09 UTC
From: vahe at spir dot me Assigned:
Status: Not a bug Package: *Math Functions
PHP Version: Irrelevant OS: Debian GNU/Linux 5.0.5 (lenny)
Private report: No CVE-ID: None
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From: vahe at spir dot me
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 [2010-09-20 13:25 UTC] vahe at spir dot me 
Description:
------------
After adding 10 times 0.1 and casting it into int or flooring it return value is 0 
instead of 1.

Test script:
---------------
$a = 0.1+0.1+0.1+0.1+0.1+0.1+0.1+0.1+0.1+0.1;

print $a; // 1
print round($a); // 1
print (int)$a; // 0 instead of 1
print floor($a); // 0 instead of 1

var_dump($a); // float(1)

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 [2010-09-20 17:09 UTC] rasmus@php.net
-Status: Open +Status: Bogus
 [2010-09-20 17:09 UTC] rasmus@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.

.
 
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