| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Craig Ringer <craig(at)2ndquadrant(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Reliance on undefined behaviour in << operator |
| Date: | 2015-09-16 19:57:04 |
| Message-ID: | 6201.1442433424@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Wed, Sep 16, 2015 at 3:16 AM, Craig Ringer <craig(at)2ndquadrant(dot)com> wrote:
>> Our implementation of << is a direct wrapper around the C operator. It
>> does not check the right-hand side's value.
>> ... On x64 intel gcc linux it does a rotation but that's
>> not AFAIK guaranteed by anything, and we should probably not be
>> relying on this or exposing it at the user level.
> I agree.
As far as I'm concerned, what those operators mean is "whatever your
compiler makes them mean". This is hardly the only place where we expose
platform-dependent behavior --- see also locale dependencies, timezones,
floating point, yadda yadda --- and I do not find it the most compelling
place to start reversing that general approach.
regards, tom lane
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