strange behavior, when converting float to int

Hi, all!

Is this a bug?

max@maximus:~$ /usr/bin/php 1.php
45
45
float(46)


max@maximus:~$ /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


max@maximus:~$ 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);

max@maximus:~$

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

> Hi, all!
>
> Is this a bug?
>
> max@maximus:~$ /usr/bin/php 1.php
> 45
> 45
> float(46)
>
>
> max@maximus:~$ /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
>
>
> max@maximus:~$ 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);
>
> max@maximus:~$


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

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/p...disclaimer.htm

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 7.999999
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
thiago.pojda@softpartech.com.br
Excelência em Softwares Financeiros

-----Mensagem original-----
De: Philip Thompson [mailto:philthathril@gmail.com]
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?
>
> max@maximus:~$ /usr/bin/php 1.php
> 45
> 45
> float(46)
>
>
> max@maximus:~$ /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
>
>
> max@maximus:~$ 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);
>
> max@maximus:~$


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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