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Date: Sat, 4 Apr 2015 00:13:29 +0300
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To: Andrea Faulds <ajf@ajf.me>
Cc: PHP Internals <internals@lists.php.net>, Nikita Popov <nikita.ppv@gmail.com>
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Subject: Re: Fix division by zero to throw exception
From: dmitry@zend.com (Dmitry Stogov)

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On Fri, Apr 3, 2015 at 11:59 PM, Andrea Faulds <ajf@ajf.me> wrote:

> Hi,
>
> > On 3 Apr 2015, at 20:46, Dmitry Stogov <dmitry@zend.com> wrote:
> >
> > May be you'll also suggest something regarding bitwise shifts with
> negative offset?
> > Allowing negative offsets using opposite directions would fix
> inconsistency, but I remember, you didn't like it.
> > May be keep WARNING (Bit shift by negative number) and then perform
> shift in another direction?
> > + disable negative shifts at compile-time.
>
> I don=E2=80=99t think opposite-direction shifts would work well for a few=
 reasons.
> I don=E2=80=99t believe this is normal behaviour in other languages, for =
one.
> Another issue is that << and >> are not actually opposites, they have
> different behaviour with respect to signs, so there=E2=80=99d be ambiguit=
y as to
> what $x << -$y means (is it the same as $x >> $y, or does it deal
> differently with signs?). Negative shifts being used are usually the resu=
lt
> of mistakes, as well, so you want to inform the user.
>
> The main problem, though, is that we previously did something different i=
f
> the shift is negative. Having it now produce a warning, means you=E2=80=
=99ll see
> error messages when you run existing code. But shifting in the opposite
> direction might change the behaviour of existing code silently
>
> I think the most sensible solution would be to make negative shifts
> produce an exception, since they=E2=80=99re really an error, an unsupport=
ed
> operation. I made them be a warning + return FALSE just because it matche=
d
> division. But that=E2=80=99s not ideal and I=E2=80=99d be fine if it was =
replaced.
>

OK. Exception is fine.

So the summary:

1) division by zero produces a warning and +/-INF IS_DOUBLE. Compile-time
evaluation is disabled.

2) Negative shift produces Exception.Compile-time evaluation is disabled.

3) Modulo by zero produces Exception.Compile-time evaluation is disabled.

Everything right?

I'm going to implement this on Monday.

Thanks. Dmitry.


>
> Thanks.
>
> --
> Andrea Faulds
> http://ajf.me/
>
>
>
>
>

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