Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:120978
Message-ID: <9a19120d-1767-6214-c728-c67a9a98f977@bastelstu.be>
Date: Mon, 4 Sep 2023 20:23:13 +0200
MIME-Version: 1.0
Content-Language: en-US
To: =?UTF-8?Q?Alexandru_P=c4=83tr=c4=83nescu?= <drealecs@gmail.com>
Cc: Jorg Sowa <jorg.sowa@gmail.com>, PHP internals <internals@lists.php.net>
References: <CAPTD5yEcwBNUe2Y9vvmHaigFtvRixJ0anTuLk4zXOKvBhrUOig@mail.gmail.com>
 <7f23f0ac-bba6-5997-b737-2a252205cf85@bastelstu.be>
 <CAAwdEzDGa+16bc0Hhmnzau6vkGpfRFqiRetw7V7KGbjsTyS8Cg@mail.gmail.com>
In-Reply-To: <CAAwdEzDGa+16bc0Hhmnzau6vkGpfRFqiRetw7V7KGbjsTyS8Cg@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Subject: Re: [PHP-DEV] [RFC] [Discussion] Add 4 new rounding modes to round()
 function
From: tim@bastelstu.be (=?UTF-8?Q?Tim_D=c3=bcsterhus?=)

Hi

On 9/3/23 17:50, Alexandru Pătrănescu wrote:
> I believe consistency is important and using UP for "away from zero" and
> DOWN for "towards zero" sounds good to me. That was so far used
> consistently everywhere, as far as I'm aware.
> Documentation is very clear about what they mean, and you can always think
> that both positive infinity and negative infinity are up while zero is down.

I believe that the code should be easy to understand without needing to 
consult the documentation. I don't find it obvious at all that "up" 
would be the infinity with the same signum rather than the positive 
infinity. This would likely be something I would need to look up all the 
time.

In fact, let me quote from the Wikipedia article linked in the RFC:

https://en.wikipedia.org/wiki/Rounding#Rounding_half_up

 > However, some programming languages (such as Java, Python) define 
their half up as round half away from zero here.

Rounding "up" in Wikipedia is defined as rounding towards positive infinity:

https://en.wikipedia.org/wiki/Rounding#Rounding_up

 > round up (or take the ceiling, or round toward positive infinity): y 
is the smallest integer that is not less than x.

I'd also like to refer to this exchange of Mastodon regarding a very 
similar issue with PHP 8.3's new IntervalBoundary enum:

https://phpc.social/@asgrim/109318512018298154

The terminology "closed" and "open" matches the standard terminology in 
maths, but without the necessary background in maths it is not obvious 
and indeed "inclusive" and "exclusive" might've been easier to 
understand for everyone, including mathematicians [1].

In this case of rounding the existing behavior of "up" meaning "towards 
the same-signum infinity" rather than "positive infinity" appears to 
even contradict the definition used by Wikipedia which I also expect to 
be the mathematical definition (but I'm happy to be corrected here). 
"Away from zero" should be clear to everyone with a basic understanding 
of English.

Introducing a brand-new RoundingMode enum (using union types) I 
suggested in my first email would nicely solve the naming problem and 
would also make the API more obvious to use due to stronger typing in 
the long run.

> Yes, we can have some extra constants for the four ones that contain "up"
> or "down" with "away from zero" and "towards zero", but I find it
> unnecessary.

Best regards
Tim Düsterhus

[1] Back then I didn't have the energy to create a follow-up RFC and now 
it's definitely too late. At least the naming is mathematically accurate.