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Date: Tue, 28 Jul 2015 07:10:50 +0900
Message-ID: <CAGa2bXaWu5uaa2kRvrmnO-JWsCq-uTeQUCNGvafOqHi4c4D7AA@mail.gmail.com>
To: Anthony Ferrara <ircmaxell@gmail.com>
Cc: Jakub Zelenka <bukka@php.net>, "internals@lists.php.net" <internals@lists.php.net>
Content-Type: multipart/alternative; boundary=001a113bcfa0d8e5ad051be2a226
Subject: Re: [PHP-DEV] json_decode/encode should return full precision values
 by default
From: yohgaki@ohgaki.net (Yasuo Ohgaki)

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Content-Type: text/plain; charset=UTF-8

Hi Anthony,

On Tue, Jul 28, 2015 at 6:54 AM, Anthony Ferrara <ircmaxell@gmail.com>
wrote:

> On Sun, Jul 26, 2015 at 4:20 PM, Yasuo Ohgaki <yohgaki@ohgaki.net> wrote:
> > Hi Jakub,
> >
> > On Mon, Jul 27, 2015 at 3:32 AM, Jakub Zelenka <bukka@php.net> wrote:
> >
> >> I don't think that this is a bug. Your example is also completely
> >> unrelated to json because the place when the value is rounded is
> var_dump
> >> where it's based on ini precision. You would get the same values with
> >> json_encode but it's only because it uses the same ini ( precision ).
> >> Basically it has nothing to do with json_decode.
> >>
> >
> > OK. Better example.
> >
> > [yohgaki@dev PHP-master]$ ./php-bin
> > <?php
> > $j = '{ "v": 0.1234567890123456789 }';
> > var_dump(json_encode(json_decode($j)));
> > ini_set('precision', 20);
> > var_dump(json_encode(json_decode($j)));
> > ?>
> >
> >
> > string(22) "{"v":0.12345678901235}"
> > string(28) "{"v":0.12345678901234567737}"
>
> I think you missed the point. Parsing isn't dependent upon precision
> setting. Only dumping: http://3v4l.org/48VSt
>
> $j = '{ "v": 0.1234567890123456789 }';
> $d1 = json_decode($j);
>
> ini_set('precision', 20);
>
> $d2 = json_decode($j);
>
> var_dump($d1, $d2);
>
> //object(stdClass)#1 (1) { ["v"]=> float(0.12345678901234567737) }
> //object(stdClass)#2 (1) { ["v"]=> float(0.12345678901234567737) }
>
> Meaning that it's parsed correctly.
>
> There is no bug here.


I understands PHP uses pure IEEE data and arithmetic and
I disagree that this is not a bug.

What I'm pointing it out is "simple JSON operation truncates
_valid/precise_ value".
IEEE double can store 17 digit fraction part precisely, but PHP truncates
it.

> <?php
> $j = '{ "v": 0.1234567890123456789 }';
> var_dump(json_encode(json_decode($j)));
> ini_set('precision', 20);
> var_dump(json_encode(json_decode($j)));
> ?>
>
>
> string(22) "{"v":0.12345678901235}"
> string(28) "{"v":0.12345678901234567737}"

The same problem in serialize/unserialize was fixed as a bug.
Encode/decode should be as precise as possible by _default_. IMO.

What's the point of truncation and having broken value?

Regards,

--
Yasuo Ohgaki
yohgaki@ohgaki.net

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