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Bug #50398 convert float to int causes an error
Submitted: 2009-12-07 12:40 UTC Modified: 2009-12-07 12:48 UTC
From: blanca at netvision dot net dot il Assigned:
Status: Not a bug Package: Unknown/Other Function
PHP Version: 5.3.1 OS: windows xp
Private report: No CVE-ID: None
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 [2009-12-07 12:40 UTC] blanca at netvision dot net dot il 
Description:
------------
when converting 12.999999999999999 from float to int,
the output is 12

but, when converting 12.9999999999999999 from float to int,
the output is 13 

Reproduce code:
---------------
$a=12.9999999999999999;
$b=(int)$a;
$a=12.999999999999999;
$c=(int)$a;
$str="\$b is: ".$b." and \$c is: ".$c;
echo $str;

Expected result:
----------------
$b is: 12 and $c is: 12

Actual result:
--------------
$b is: 13 and $c is: 12

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 [2009-12-07 12:48 UTC] johannes@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.

The docs say

"When converting from float to integer, the number will be rounded towards zero."

http://php.net/manual/en/language.types.integer.php#language.types.integer.casting

Now combining this with the unprecise nature of floating point numbers this gives "random" results.
 
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