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Date: Thu, 17 Jul 2014 11:24:42 +0200
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To: Sara Golemon <pollita@php.net>
Cc: Andrea Faulds <ajf@ajf.me>, bishop@php.net, PHP internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary=089e010d8c7af1627f04fe60355e
Subject: Re: [PHP-DEV] [RFC] intdiv()
From: nikita.ppv@gmail.com (Nikita Popov)

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On Thu, Jul 17, 2014 at 2:25 AM, Sara Golemon <pollita@php.net> wrote:

> On Wed, Jul 16, 2014 at 8:15 AM, Andrea Faulds <ajf@ajf.me> wrote:
> > Nikita Popov doesn=E2=80=99t seem to be a fan of the %% syntax, so it m=
ay be
> subject to change, though I think it=E2=80=99s the best I=E2=80=99ve hear=
d so far. ;)
> >
> Nor am I.  Here's a thought though: How about just making / return int
> when there's no remainder.
>
> Looking at this code, you might think it's inefficent:
>
> double dres =3D a / b;
> long lres =3D a / b;
> if (a % b) {
>   return dres;
> } else {
>   return lres;
> }
>
> But in fact at -O1, gcc will optimize this (probably clang and others
> as well) to a single idivq instruction and only do the cvtsi2sdq in
> the dres case.
>
> My point being, we can just make division with an integral result
> return a result of integer division without altering the syntax or
> adding a perf hit.
>

This is already what is currently happening, see
http://lxr.php.net/xref/PHP_TRUNK/Zend/zend_operators.c#1067.

Andreas proposal is only useful in the case that the numbers don't divide
exactly and you need round-down/truncation behavior and your numbers are in
a range where the indirection through double arithmetic results in
precision loss.

Nikita

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