Re: C standard compliance?

From: David Kastrup <dak@gnu.org>
Date: Jan 29, 2014, 20:52 UTC
Message-ID: <87eh3q5x42.fsf@fencepost.gnu.org>
In-Reply-To: <xmqqwqhiikpg.fsf@gitster.dls.corp.google.com>

Junio C Hamano <gitster@pobox.com> writes:

Show 13 quoted lines

> 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