From: David Kastrup <dak@gnu•org>
To: Junio C Hamano <gitster@pobox•com>
Cc: git@vger•kernel.org
Subject: Re: C standard compliance?
Date: Wed, 29 Jan 2014 21:52:45 +0100 [thread overview]
Message-ID: <87eh3q5x42.fsf@fencepost.gnu.org> (raw)
In-Reply-To: <xmqqwqhiikpg.fsf@gitster.dls.corp.google.com> (Junio C. Hamano's message of "Wed, 29 Jan 2014 12:42:19 -0800")
Junio C Hamano <gitster@pobox•com> writes:
> 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.
The types intptr_t and uintptr_t are optional in ISO/IEC 9899:1999
(C99). So it would seem that I'd be covering fewer cases rather than
more in that manner.
I should think that architectures providing uintptr_t/intptr_t would
have very little incentive _not_ to offer pointer inequalities
equivalent to either the uintptr_t or intptr_t type conversion.
--
David Kastrup
next prev parent reply other threads:[~2014-01-29 20:53 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
2014-01-29 20:52 ` David Kastrup [this message]
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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