From: "David Kastrup" <>
Junio C Hamano <> writes:

David Kastrup <> 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
pointers into the same structure) to allow for some cheapskate sort
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.

Undefined behaviours become hidden bugs of the future...

"blog on the problems of unexpected optimization bugs,
such as dereferencing a null pointer. "Finding Undefined Behavior Bugs
by Finding Dead Code" which links to
the draft of an interesting paper";

The code has now been released, and a few potential errors in Git were caught by that tool by Stefan Beller.

The key point of the paper was never to try to use an 'obvious', but
undefined, behaviour.


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