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Date: Sat, 4 Apr 2015 01:08:14 +0300
Message-ID: <CA+9eiLvkiMNjbrDA1tjO4xuhbFGoY2buP6n6ZNrtHR5qWLZ0RQ@mail.gmail.com>
To: Nikita Popov <nikita.ppv@gmail.com>
Cc: PHP Internals <internals@lists.php.net>, Andrea Faulds <ajf@ajf.me>
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Subject: Re: Fix division by zero to throw exception
From: dmitry@zend.com (Dmitry Stogov)

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On Apr 4, 2015 12:34 AM, "Nikita Popov" <nikita.ppv@gmail.com> wrote:
>
> On Fri, Apr 3, 2015 at 11:13 PM, Dmitry Stogov <dmitry@zend.com> wrote:
>>
>>
>>
>>
>> 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 f=
ew
reasons. I don=E2=80=99t believe this is normal behaviour in other language=
s, 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 re=
placed.
>>
>>
>> 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?
>
>
> Don't think we need to disable compile-time evaluation for 2) and 3).
It'll just end up being a compile error in that case. I think if you have 1
% 0 occurring in your code literally, it's better to have the compile fail
rather than getting (or not getting) a runtime exception.

This is even easier.
Andrea, what do you think?

Thanks. Dmitry.

>
> Nikita
>

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