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Re: [css3-values] Required minimum precision

From: Boris Zbarsky <bzbarsky@MIT.EDU>
Date: Thu, 28 Jun 2012 15:37:04 -0400
Message-ID: <4FECB260.4090705@mit.edu>
To: www-style@w3.org
On 6/28/12 3:21 PM, Tab Atkins Jr. wrote:
> During the last telcon, we claimed that we hadn't posted our proposal
> for required minimum precision.  We're dumb - it was already in the
> draft:<http://dev.w3.org/csswg/css3-values/#limits>.
> So, we need to either approve this, edit it, or defer it to level 4.
> Thoughts?  Can implementors please take a look and let us know if
> these limits are acceptable minimums?

Two questions:

1)  Where does an absolute value of (2^24)-1 come from?  Since this is 
talking about signed quantities, it's requiring that at least 25 bits be 
used to represent them, which is a slightly odd behavior.  Was this 
supposed to use (2^23)-1 ?

2)  Implementing the "except that values that are not equal to, but 
would round to, either zero or the boundary of a closed range, are 
rounded away from that value rather than to it." might be rather 
difficult.  Consider a decimal value like 
0.99999999999999999999999999999999999999999999 which will give you 1.0 
when converted to an IEEE double, for example.  The only way I see to 
avoid this becoming 1.0 is for the UA to reinvent the string-to-double 
wheel in a way that allows the rounding behavior described in the spec 
(and in particular, in a way that does not make use of existing 
string-to-double libraries, which do not have any such behavior 
defined).  In this particular case the UA could add a hack like "check 
the first digit", but things get more complicated if we add scientific 
notation or calc().  I'm not quite sure what the best course of action 
here is....

Received on Thursday, 28 June 2012 19:37:34 UTC

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