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Date: Fri, 3 Apr 2015 21:59:33 +0100
Cc: PHP Internals <internals@lists.php.net>,
 Nikita Popov <nikita.ppv@gmail.com>
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References: <CA+9eiLvd0YPKtED9CgU_thC9HUfTquaMJNf_9zQC0jyeX+rTuw@mail.gmail.com> <33BCE1D0-BA6D-464C-B23D-69AF71356111@ajf.me> <CA+9eiLsEDb-GuP4pRi-C8GQ2N+q7K=f-gmUMMxzxyy54CDy67w@mail.gmail.com>
To: Dmitry Stogov <dmitry@zend.com>
Subject: Re: Fix division by zero to throw exception
From: ajf@ajf.me (Andrea Faulds)

Hi,

> On 3 Apr 2015, at 20:46, Dmitry Stogov <dmitry@zend.com> wrote:
>=20
> 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 ambiguity 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 result of mistakes, as well, so you want to =
inform the user.

The main problem, though, is that we previously did something different =
if 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 =
unsupported operation. I made them be a warning + return FALSE just =
because it matched division. But that=E2=80=99s not ideal and I=E2=80=99d =
be fine if it was replaced.

Thanks.=20

--
Andrea Faulds
http://ajf.me/