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To: "Nicolas Grekas" <nicolas.grekas+php@gmail.com>,
	<internals@lists.php.net>
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Date: Wed, 9 Feb 2011 01:10:18 +0200
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Subject: Re: [PHP-DEV] Change default serialize precision from 100 to 17
From: sv_forums@fmethod.com ("Stan Vass")

>> ini_set('precision', 17);
>
> After some testings, here is what I get :
>
> <?php
>
> ini_set('precision', 14);
> echo 0.1; // 0.1
> echo 0.2; // 0.2
> echo 0.3; // 0.3
>
> ini_set('precision', 17);
> echo 0.2; // 0.10000000000000001
> echo 0.2; // 0.20000000000000001
> echo 0.3; // 0.29999999999999999
>
> ?>
>
> The default precision of 14 (or 12) must have been chosen to address
> this overlong string representation of many simple floats ?
> While I agree with you that any data loss must be forbidden, couldn't
> this also break existing code ?
> Would it be possible to "displays a value based on the shortest
> decimal fraction that rounds correctly back to the true binary value",
> like python 2.7 and 3.1 do ?
> (http://docs.python.org/tutorial/floatingpoint.html)
>
> Just my 2cts :)
>
> Nicolas

As I've shown in the previous post, "looks better" doesn't mean "is more 
accurate". It's true that precision has been set to 12 or 14 in order to 
look better with some small decimal fractions, but that can't be the only 
concern when that same precision is used also for serialization during 
database escaping.

It's hard to imagine when the display precision of an echoed float being 
longer or less aesthetically pleasing to a human eye may break code, but 
when real precision is lost, and this is sent to the database like that, 
this is a much more tangible problem.

In terms of formatting of floats for humans, we still have printf() and 
number_format(), which allow control independent of the ini setting (which 
people use when they need that explicit control).

Stan Vass