From: Jamie Lokier <jamie@shareable.org>
To: Chip Salzenberg <chip@pobox.com>
Cc: Willy Tarreau <willy@w.ods.org>,
Albert Cahalan <albert@users.sourceforge.net>,
linux-kernel mailing list <linux-kernel@vger.kernel.org>,
davem@redhat.com
Subject: Re: [PATCH] 2.4.22pre10: {,un}likely_p() macros for pointers
Date: Mon, 11 Aug 2003 05:30:56 +0100 [thread overview]
Message-ID: <20030811043056.GG10446@mail.jlokier.co.uk> (raw)
In-Reply-To: <20030811023912.GJ24349@perlsupport.com>
Chip Salzenberg wrote:
> > It's portable as long as the compiler is GCC :)
> No; wrong; please pay attention.
I was being facetious :)
> Both parameters of __builtin_expect() are long ints.
So it is broken if passed a "long long"? The documentation says "you
are limited to integral expressions".
...You're right. The documentation is wrong. It's strictly takes
"long int" arguments and returns a long.
> On an architecture where there's a pointer type larger than long[1],
> __builtin_expect() won't just warn, it'll *fail*.
A pointer really should fail on all architectures.
Fortunately you do get a warning.
> Also, on an architecture where a conversion of a null pointer to
> long results in a non-zero value[2], it'll *fail*. That makes it
> non-portable twice over. Wouldn't you agree?
[2] - I don't believe such architectures are supported by GCC, hence
the facetious comment.
> Since you are limited to integral expressions for exp, you should use constructions such as
>
> if (__builtin_expect (ptr != NULL, 1))
> error ();
>
> when testing pointer or floating-point values.
I think we all agree with this.
-- Jamie
next prev parent reply other threads:[~2003-08-11 4:31 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-08-10 4:03 [PATCH] 2.4.22pre10: {,un}likely_p() macros for pointers Albert Cahalan
2003-08-10 7:29 ` Willy Tarreau
2003-08-10 8:02 ` Willy Tarreau
2003-08-11 1:23 ` Chip Salzenberg
2003-08-11 2:09 ` Jamie Lokier
2003-08-11 2:39 ` Chip Salzenberg
2003-08-11 4:02 ` Albert Cahalan
2003-08-11 4:30 ` Jamie Lokier [this message]
2003-08-11 5:30 ` Willy Tarreau
2003-08-11 5:42 ` Jamie Lokier
2003-08-11 13:09 ` Albert Cahalan
2003-08-11 18:55 ` Andrew Morton
2003-08-11 23:13 ` Albert Cahalan
2003-08-13 19:42 ` Jamie Lokier
2003-08-11 4:55 ` Jamie Lokier
2003-08-11 5:26 ` Willy Tarreau
2003-08-11 5:38 ` Jamie Lokier
-- strict thread matches above, loose matches on Subject: below --
2003-08-05 12:44 Albert Cahalan
2003-08-09 0:21 ` Jamie Lokier
2003-08-09 8:13 ` Willy Tarreau
2003-08-09 8:51 ` David S. Miller
2003-08-09 9:36 ` Jamie Lokier
2003-08-09 10:10 ` Herbert Xu
2003-08-09 10:42 ` Alan Cox
2003-08-09 16:23 ` Jamie Lokier
2003-08-04 17:06 Chip Salzenberg
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