Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:46733
Mailing-List: contact internals-help@lists.php.net; run by ezmlm
Received-SPF: error (pb1.pair.com: domain analysisandsolutions.com from 166.84.1.72 cause and error)
Date: Thu, 14 Jan 2010 13:32:57 -0500
To: Ralph Schindler <ralph@smashlabs.com>
Cc: internals <internals@lists.php.net>
Message-ID: <20100114183257.GA28492@panix.com>
References: <4B4E658C.7080908@smashlabs.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <4B4E658C.7080908@smashlabs.com>
User-Agent: Mutt/1.5.18 (2008-05-17)
Subject: Re: [PHP-DEV] Int to float precision loss in 64bit environment
From: danielc@analysisandsolutions.com (Daniel Convissor)

Hi Ralph:

On Wed, Jan 13, 2010 at 06:30:04PM -0600, Ralph Schindler wrote:
> In talking with Stas, it seems that since PHP_INT_MAX+1 is pushed into a  
> (float) and since float values are stuffed into 52bit mantissa / 11 bits  
> for exponents, we are loosing some precision.  That lost precisions is  
> causing the above to fail in one platform, and work in another.
>
> Is this noted somewhere?  Is there a workaround? Or, is this something  
> that can be fixed for 64 bit platforms (somehow)?

It's not really documented, that I've seen.  I'll put this on my todo 
list.

There was a discussion about this in March/April of last year.  In short, 
it's not easily fixable.  Christian Seiler's post on 2009-04-07 is very 
interesting.  The MARC archive split the thread in two:

http://marc.info/?t=123704116800002&r=1&w=2
http://marc.info/?t=123865732900002&r=1&w=2

I imagine the workarounds are the BC Math and GMP functions.

--Dan

-- 
 T H E   A N A L Y S I S   A N D   S O L U T I O N S   C O M P A N Y
            data intensive web and database programming
                http://www.AnalysisAndSolutions.com/
 4015 7th Ave #4, Brooklyn NY 11232  v: 718-854-0335 f: 718-854-0409