Re: [Bimi] [rfc-i] SVG P/S Feedback

["Martin J. Dürst" <[e-mail]>]

Hello Brian, others,

On 31/08/2020 08:36, Brian E Carpenter wrote:
> On 31-Aug-20 10:09, Leonard Rosenthol wrote:
>> Brian - not sure what you are looking at, but in SVG 1.1 (https://www.w3.org/TR/SVG11/single-page.html#types-DataTypeNumber), I see the following definition for a `<number>`

[snip]

> Yes, and that's all fine. But when you start converting formats, and the round trip converts
> 32.459999 into 32.424, there's clearly a problem of how real numbers work in a particular hardware and floating point library, and/or a difference in how real numbers are handled in the two formats. So specifying how real numbers are represented in various SGML dialects is only part of the problem.
> 
> I'm no expert on this, but https://en.wikipedia.org/wiki/IEEE_754 tells me that it's very complex and there are many cans of worms.

Floating point numbers are what they are, even if many people, including 
engineers, tend to ignore or suppress the details.

The programming language Ruby has some pointers to information about 
floating point numbers on the otherwise quite small top page of their 
bug tracker (https://bugs.ruby-lang.org/). The reason for this is the 
frequency with which we get bug reports about floating point number 
calculations that turn out not to be bugs.

For people interested in details, I suggest reading "What Every Computer 
Scientist Should Know About Floating-Point Arithmetic"
(https://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html).

Btw, if a conversion changes 32.459999 into 32.424, then we indeed have 
a serious problem. Floating point arithmetic isn't that inaccurate, even 
on the worst hardware. If the conversion is from 32.459999 to 32.46, on 
the other hand, then that's entirely possible, and shouldn't create any 
problems in patent litigation.

Regards,   Martin.


> Regards
>      Brian