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RE: [SVGMobile12] uDOM attribute normalization and getAttribute

From: Jon Ferraiolo <jonf@adobe.com>
Date: Thu, 19 Jan 2006 16:38:08 -0800
Message-ID: <6ECA24BE410D994496A2AE995367C5C85D5B2F@namail3.corp.adobe.com>
To: "Bjoern Hoehrmann" <derhoermi@gmx.net>
Cc: <www-svg@w3.org>

I don't think user agents will go out of their way to represent "3.0" as "3.04", but SVG Tiny user agents are likely to normalize some floating point values. SVG Tiny user agents typically use 16:16 fixed point approaches (i.e., 16 bits for mantissa including sign, 16 bits for exponent including sign) or 4-byte IEEE floating point. (See Number type in http://www.w3.org/TR/SVGMobile/#sec-data-types). For SVG on mobile devices, memory requirements are dominated by the coordinate values on path data. The most important memory savings is achieved by using the minimal amount of memory to store the path coordinates. This drove the decision to allow user agents normalize the values that they store (path data or otherwise).

In either case (fixed or float), there is a distinct possibility of round-off.


-----Original Message-----
From: Bjoern Hoehrmann [mailto:derhoermi@gmx.net] 
Sent: Thursday, January 19, 2006 3:17 PM
To: Jon Ferraiolo
Cc: www-svg@w3.org
Subject: Re: [SVGMobile12] uDOM attribute normalization and getAttribute

* Jon Ferraiolo wrote:
>No, that's not what normalization means in this context. It isn't
>forcing a particular reproducible result; in fact, it is going in the
>other direction. It is allowing a user agent to normalize according to
>its own requirements, and thereby possibly changing the value. For
>example, '45.57' via a setter might come back as '45.6' or '45.5698' via
>a getter.

While I am not sure how this would necessarily violate my constraints,
I must say this is an interesting interpretation of the definition-by-
example in the draft: "Numerical precision: "3.0" may be returned as
"3", "3.00" or other semantically identical form". Who would have
thought that other semantically identical forms of 3.0 include 3.04
and 2.96 if that suits the user agent.
Björn Höhrmann · mailto:bjoern@hoehrmann.de · http://bjoern.hoehrmann.de
Weinh. Str. 22 · Telefon: +49(0)621/4309674 · http://www.bjoernsworld.de
68309 Mannheim · PGP Pub. KeyID: 0xA4357E78 · http://www.websitedev.de/ 
Received on Friday, 20 January 2006 00:36:40 UTC

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