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Date: Thu, 17 Jul 2014 09:51:54 +0800
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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=047d7b3a98d0a79e7404fe59e206
Subject: Re: [PHP-DEV] [RFC] intdiv()
From: tjerk.meesters@gmail.com (Tjerk Meesters)

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Hi Sara,

On Thu, Jul 17, 2014 at 8:25 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.
>

Just out of curiosity, does the compiler optimise it into something like
this?

if (a % b) {
  return a / b;
} else {
  return (double)a / b;
}

Or, would writing it like that skip the optimisation of being able to fetch
the division result from %rax?


> 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.
>
> -Sara
>
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>


--=20
--
Tjerk

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