Re: Improving JSON pretty printing, how to represent floats?

[Herman , Géza]

Eli Zaretskii <eliz@gnu.org> writes:

> > From: Herman, Géza <geza.herman@gmail.com>
> > Date: Fri, 05 Apr 2024 11:39:10 +0200
> >
> > There is a thing that I don't like about the current
> > json-pretty-print: as it parses floats, pretty printing can be
> > lossy.  If one pretty prints this
> >
> > --8<---------------cut 
> > here---------------start------------->8---
> > {
> >     "a": 3.333333333333000000000000000001
> > }
> > --8<---------------cut 
> > here---------------end--------------->8---
> >
> > then the float gets rounded.  I think pretty printing should be
> > lossless (keeping the exact format, exp notation, etc.).
>
> The digits in 3.333333333333000000000000000001 after 16th digit 
> are
> meaningless: they aren't supported by IEEE floating-point 
> standard, so
> they are just numerical noise.  Thus, talking about "lossless" 
> wrt
> them makes little sense to me.

You mean the 64-bit binary format. IEEE-754 describes more formats 
which have more precision, and also there are more formats used in 
practice than what IEEE-754 describes.

Plus, I don't think that the JSON standard mandates IEEE-754 
numbers.  It just describes numbers, so I think it's good behavior 
to not change numbers during formatting.