"brian m. carlson" <sand...@crustytoothpaste.net> writes:
> On Wed, Jan 29, 2014 at 09:52:45PM +0100, David Kastrup wrote:
>> Junio C Hamano <gits...@pobox.com> writes:
>> > 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 think we already use uintptr_t in the codebase, and if it's not
> present, we typedef it to unsigned long. So I think it should be fine
> (and well-defined) if instead of doing
> void *p, *q;
> if (p < q)
> you do:
> void *p, *q;
> if ((uintptr_t)p < (uintptr_t)q)
> Then on those systems where the compiler has some bizarre undefined
> behavior checking, the code will work. On systems that don't have
> uintptr_t, the compiler is probably not smart enough to perform such a
> check anyway.
The use case is actually sorting a list such that entries pointing to
the same malloced "origin" data structure are in adjacent list
positions. At list intptr_t seems used plentifully in Git.
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