From: Junio C Hamano <gitster@pobox•com>
To: David Kastrup <dak@gnu•org>
Cc: git@vger•kernel.org
Subject: Re: C standard compliance?
Date: Wed, 29 Jan 2014 12:42:19 -0800 [thread overview]
Message-ID: <xmqqwqhiikpg.fsf@gitster.dls.corp.google.com> (raw)
In-Reply-To: <87iot25y0r.fsf@fencepost.gnu.org> (David Kastrup's message of "Wed, 29 Jan 2014 21:33:08 +0100")
David Kastrup <dak@gnu•org> writes:
> Hi, I am wondering if I may compare pointers with < that have been
> created using different calls of malloc.
>
> The C standard does not allow this (inequalities are only allowed for
> pointers into the same structure) to allow for some cheapskate sort of
> comparison in segmented architectures.
Hmm... if you were to implement a set of pointers in such a way that
you can cheaply tell if an unknown pointer belongs to that set, you
would use a hashtable, keyed with something that is derived from the
value of the pointer casted to uintptr_t, I would think. Is such a
use of ((uintptr_t)ptr) unallowed? If it is allowed, comparing two
unrelated pointers after casting them to uintptr_t would equally be
valid, I would have to think.
next prev parent reply other threads:[~2014-01-29 20:42 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-29 20:33 C standard compliance? David Kastrup
2014-01-29 20:42 ` Junio C Hamano [this message]
2014-01-29 20:52 ` David Kastrup
2014-01-29 23:00 ` Philip Oakley
2014-01-29 23:33 ` brian m. carlson
2014-01-30 0:02 ` David Kastrup
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