Signed word lengths and indexes

["Jérôme M. Berger"]

Jérôme M. Berger wrote:
> Walter Bright wrote:
>> Jérôme M. Berger wrote:
>>>     Actually, that problem already occurs in C. I've had problems when
>>> porting code from x86 to x86_64 because some unsigned operations
>>> don't behave the same way on both...
>> How so? I thought most 64 bit C compilers were specifically designed to
>> avoid this problem.
> 
> 	I can't isolate it to a minimal test case, but at my job, we make
> an image processing library. Since negative image dimensions don't
> make sense, we decided to define width and height as "unsigned int".
> Now, we have code that works fine on 32-bit platforms (x86 and arm)
> but segfaults on x86_64. Simply adding an (int) cast in front of the
> image dimensions in a couple of places fixes the issue (tested with
> various versions of gcc on linux and windows).
> 
	Gotcha! See the attached test case. I will post the explanation for
the issue as a reply to give everyone a chance to try and spot the
error...

		Jerome
-- 
mailto:jeberger at free.fr
http://jeberger.free.fr
Jabber: jeberger at jabber.fr
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