[PHP] strange behavior, when converting float to int

[Maxim Antonov]

Hi, all!

Is this a bug?

[EMAIL PROTECTED]:~$ /usr/bin/php 1.php
45
45
float(46)


[EMAIL PROTECTED]:~$ /usr/bin/php -v
PHP 5.3.0-dev (cli) (built: Apr  4 2008 11:37:33)
Copyright (c) 1997-2008 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2008 Zend Technologies


[EMAIL PROTECTED]:~$ cat 1.php
?php
$i = 10.35 + 20.76 + 5.80 + 5.80 + 3.29;
echo (int)$i;
echo \n;
echo intval($i);
echo \n;
var_dump($i);

[EMAIL PROTECTED]:~$


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Re: [PHP] strange behavior, when converting float to int

[Philip Thompson]

On May 6, 2008, at 1:38 AM, Maxim Antonov wrote:


Hi, all!

Is this a bug?

[EMAIL PROTECTED]:~$ /usr/bin/php 1.php
45
45
float(46)


[EMAIL PROTECTED]:~$ /usr/bin/php -v
PHP 5.3.0-dev (cli) (built: Apr  4 2008 11:37:33)
Copyright (c) 1997-2008 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2008 Zend Technologies


[EMAIL PROTECTED]:~$ cat 1.php
?php
$i = 10.35 + 20.76 + 5.80 + 5.80 + 3.29;
echo (int)$i;
echo \n;
echo intval($i);
echo \n;
var_dump($i);

[EMAIL PROTECTED]:~$



I got the same results. I'm not exactly sure what's happening, but I'd  
be curious to see if there's anyone else who can shed some light.


PHP Version 5.2.4.

~Philip


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Re: [PHP] strange behavior, when converting float to int

[Paul Scott]

On Tue, 2008-05-06 at 09:34 -0500, Philip Thompson wrote:

 I got the same results. I'm not exactly sure what's happening, but
 I'd  
 be curious to see if there's anyone else who can shed some light.
 
 PHP Version 5.2.4.

Is this not coming from the underlying C libs that directly use the FP
on the CPU? 

I would say that the compile flags, CPU settings etc would probably have
an impact on accuracy.

--Paul

All Email originating from UWC is covered by disclaimer 
http://www.uwc.ac.za/portal/public/portal_services/disclaimer.htm 

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RES: [PHP] strange behavior, when converting float to int

[Thiago Pojda]

There is a logical explanation.

[...] you need to be aware that the float data type is not always
capable of representing numbers in the way you expect it to.

And then follows a example:
Consider, for example this simple statement:
echo (int) ((0.1 + 0.7) * 10);
You would expect that the expression ((0.1 + 0.7) * 10) would evaluate to 8
(and, in fact, if you print it out without the integer conversion, it does).
However the statement above outputs 7 instead. This happens because the
result of this simple arithmetic expression is stored internally as 7.99
instead of 8; when the value is converted to int, PHP simply truncates away
the fractional part, resulting in a rather significant error (12.5%, to be
exact). [manually typed]

Zend PHP5 Certification Guide 2nd Edition, Chapter 1 - PHP Basics, page
9-10. SHAFIK, D., RAMSEY, B. 
Ed. php|architect nanobooks


Not sure if this is what happening with you as I did not try to reproduce
your error, but looks like it. This book is good, a lot of gotchas. You
should get it :)

Regards,
Thiago Henrique Pojda
Desenvolvimento Web
+55 41 3033-7676
[EMAIL PROTECTED]
Excelência em Softwares Financeiros

-Mensagem original-
De: Philip Thompson [mailto:[EMAIL PROTECTED] 
Enviada em: terça-feira, 6 de maio de 2008 11:34
Para: PHP-General List
Assunto: Re: [PHP] strange behavior, when converting float to int

On May 6, 2008, at 1:38 AM, Maxim Antonov wrote:

 Hi, all!

 Is this a bug?

 [EMAIL PROTECTED]:~$ /usr/bin/php 1.php
 45
 45
 float(46)


 [EMAIL PROTECTED]:~$ /usr/bin/php -v
 PHP 5.3.0-dev (cli) (built: Apr  4 2008 11:37:33)
 Copyright (c) 1997-2008 The PHP Group
 Zend Engine v2.3.0, Copyright (c) 1998-2008 Zend Technologies


 [EMAIL PROTECTED]:~$ cat 1.php
 ?php
 $i = 10.35 + 20.76 + 5.80 + 5.80 + 3.29;
 echo (int)$i;
 echo \n;
 echo intval($i);
 echo \n;
 var_dump($i);

 [EMAIL PROTECTED]:~$


I got the same results. I'm not exactly sure what's happening, but I'd  
be curious to see if there's anyone else who can shed some light.

PHP Version 5.2.4.

~Philip


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