From: "Shawn O. Pearce" <spearce@spearce•org>
To: Nicolas Pitre <nico@cam•org>
Cc: Junio C Hamano <gitster@pobox•com>,
Pieter de Bie <pdebie@ai•rug.nl>,
Pierre Habouzit <madcoder@debian•org>,
git@vger•kernel.org, Scott Chacon <schacon@gmail•com>
Subject: Re: libgit2 - a true git library
Date: Fri, 31 Oct 2008 18:52:17 -0700 [thread overview]
Message-ID: <20081101015217.GJ14786@spearce.org> (raw)
In-Reply-To: <alpine.LFD.2.00.0810312135190.13034@xanadu.home>
Nicolas Pitre <nico@cam•org> wrote:
> On Fri, 31 Oct 2008, Shawn O. Pearce wrote:
>
> > > Both the negative code and errno style are lightweight in the common "no
> > > error" case. The errno style is probably more handy for those functions
> > > returning a pointer which should be NULL in the error case.
> >
> > I'm sticking with return a negative code for now, to the extent
> > that some functions which return a pointer but also have many
> > common failure modes (e.g. git_odb_open) use an output parameter
> > as their first arg, so the error code can be returned as the result
> > of the function.
>
> Actually, the pointer-returning functions can encode error cases into a
> "negative" pointer. See include/linux/err.h for example.
>
> void *ptr = git_alloc_foo(...);
> if (IS_ERR(ptr))
> die("git_alloc_foo failed: %s", git_strerr(PTR_ERR(ptr)));
Oh, good point. We could also stagger the errors so they are
always odd, and never return an odd-alignment pointer from a
successful function. Thus IS_ERR can be written as:
#define IS_ERR(ptr) (((intptr_t)(ptr)) & 1)
which is quite cheap, and given the (probably required anyway)
aligned allocation policy means we still have 2^31 possible
error codes available.
--
Shawn.
next prev parent reply other threads:[~2008-11-01 1:53 UTC|newest]
Thread overview: 83+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-10-31 17:07 libgit2 - a true git library Shawn O. Pearce
2008-10-31 17:28 ` Pieter de Bie
2008-10-31 17:29 ` Pieter de Bie
2008-10-31 17:47 ` Pierre Habouzit
2008-10-31 18:41 ` Shawn O. Pearce
2008-10-31 18:54 ` Pierre Habouzit
2008-10-31 19:57 ` Shawn O. Pearce
2008-10-31 20:12 ` Pierre Habouzit
2008-10-31 20:05 ` Junio C Hamano
2008-10-31 21:58 ` Shawn O. Pearce
2008-11-01 17:30 ` Pierre Habouzit
2008-11-01 18:44 ` Andreas Ericsson
2008-11-01 18:48 ` Pierre Habouzit
2008-11-01 20:29 ` Shawn O. Pearce
2008-11-01 21:58 ` Andreas Ericsson
2008-11-02 1:50 ` Shawn O. Pearce
2008-11-03 10:17 ` Andreas Ericsson
2008-11-02 1:56 ` Shawn O. Pearce
2008-11-02 9:25 ` Pierre Habouzit
2008-10-31 20:24 ` Nicolas Pitre
2008-10-31 20:29 ` david
2008-10-31 20:56 ` Nicolas Pitre
2008-10-31 21:43 ` Shawn O. Pearce
2008-10-31 21:50 ` Shawn O. Pearce
2008-10-31 21:51 ` Pierre Habouzit
2008-10-31 21:31 ` Pierre Habouzit
2008-10-31 22:10 ` Nicolas Pitre
2008-11-01 10:52 ` Andreas Ericsson
2008-10-31 23:24 ` Pieter de Bie
2008-10-31 23:28 ` Shawn O. Pearce
2008-10-31 23:49 ` Junio C Hamano
2008-11-01 0:02 ` Pierre Habouzit
2008-11-01 0:19 ` Shawn O. Pearce
2008-11-01 1:02 ` Pierre Habouzit
2008-11-01 0:13 ` Shawn O. Pearce
2008-11-01 1:15 ` Nicolas Pitre
2008-11-01 1:19 ` Shawn O. Pearce
2008-11-01 1:45 ` Nicolas Pitre
2008-11-01 1:52 ` Shawn O. Pearce [this message]
2008-11-01 2:26 ` Johannes Schindelin
2008-11-01 11:01 ` Pierre Habouzit
2008-11-01 13:50 ` Nicolas Pitre
2008-11-01 17:01 ` Pierre Habouzit
2008-11-01 20:26 ` Johannes Schindelin
2008-10-31 23:14 ` Junio C Hamano
2008-10-31 23:33 ` Pierre Habouzit
2008-10-31 23:41 ` Shawn O. Pearce
2008-10-31 23:56 ` Jakub Narebski
2008-11-01 0:41 ` david
2008-11-01 1:00 ` Shawn O. Pearce
2008-11-01 1:04 ` david
2008-11-01 1:08 ` Pierre Habouzit
2008-11-01 1:33 ` Nicolas Pitre
2008-11-01 1:38 ` Pierre Habouzit
2008-11-01 1:49 ` Nicolas Pitre
2008-11-01 1:43 ` Shawn O. Pearce
2008-11-01 1:53 ` Nicolas Pitre
2008-11-01 22:57 ` Shawn O. Pearce
2008-11-02 0:26 ` Scott Chacon
2008-11-02 1:07 ` Scott Chacon
2008-11-02 1:36 ` Shawn O. Pearce
2008-11-02 5:09 ` David Brown
2008-11-03 16:20 ` Shawn O. Pearce
2008-11-01 1:06 ` Pierre Habouzit
2008-11-01 1:36 ` david
2008-10-31 20:24 ` Brian Gernhardt
2008-10-31 21:59 ` Andreas Ericsson
2008-10-31 22:01 ` Shawn O. Pearce
2008-10-31 22:51 ` Junio C Hamano
2008-11-01 11:17 ` Andreas Ericsson
2008-10-31 23:22 ` Johannes Schindelin
2008-10-31 23:18 ` Bruno Santos
2008-10-31 23:25 ` Shawn O. Pearce
2008-11-01 19:18 ` Andreas Ericsson
2008-11-01 20:42 ` Shawn O. Pearce
2008-11-02 2:30 ` Johannes Schindelin
2008-11-02 9:19 ` Pierre Habouzit
2008-11-03 13:08 ` Andreas Ericsson
2008-11-08 13:26 ` Steve Frécinaux
2008-11-08 14:35 ` Andreas Ericsson
2008-11-08 17:27 ` Pierre Habouzit
2008-11-09 10:17 ` Andreas Ericsson
2008-11-09 21:02 ` Shawn O. Pearce
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