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Date: Fri, 3 Apr 2015 23:34:04 +0200
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To: Dmitry Stogov <dmitry@zend.com>
Cc: Andrea Faulds <ajf@ajf.me>, PHP Internals <internals@lists.php.net>
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Subject: Re: Fix division by zero to throw exception
From: nikita.ppv@gmail.com (Nikita Popov)

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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 fe=
w
>> reasons. I don=E2=80=99t believe this is normal behaviour in other langu=
ages, for
>> one. Another issue is that << and >> are not actually opposites, they ha=
ve
>> different behaviour with respect to signs, so there=E2=80=99d be ambigui=
ty 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 res=
ult
>> 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 unsuppor=
ted
>> operation. I made them be a warning + return FALSE just because it match=
ed
>> 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?
>

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.

Nikita

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