From: | "ktm(at)rice(dot)edu" <ktm(at)rice(dot)edu> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, 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 20:29:23 |
Message-ID: | 20150916202923.GP18476@aart.rice.edu |
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Lists: | pgsql-hackers |
On Wed, Sep 16, 2015 at 03:57:04PM -0400, Tom Lane wrote:
> 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
>
+1
I tend to agree. Unless the behavior is mandated by the SQL standard, I have
always expected the behavior of those apps to follow that defined by the
compiler.
Regards,
Ken
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