Re: [B.A.T.M.A.N.] [PATCH] batman-adv: Fixing wrap-around bug in vis

[Sven Eckelmann <sven.eckelmann@gmx.de>]

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Linus Lüssing wrote:
> Sorry still does not seem to work :). Despite testing it on a
> setup in batman itself I also tested it with a small c program
> (which does not work as expected either):

But your version works? I would really doubt that when we do the same. The
macro will only replace the thing and we would have the same formular in that
situation.

> -----
> #include <stdio.h>
> #include <stdint.h>
> 
> #define seq_before(x,y) ((x - y) > 1 << 7 + 8 * (sizeof(x) - 1))
> #define seq_after(x,y) ((y - x) >= 1 << 7 + 8 * (sizeof(x) - 1))
> 
> int main() {
>         uint8_t old = 0;
>         uint8_t new = 1;
>         if (!seq_after(new,old))
>                 printf("foobar\n");
> 
>         return 0;
> }
> -----
> $ ./test
> foobar
> $

Now it gets real cruel, but who cares... C++ wasn't accept in the kernel, so we have
to deal with it using some GNUish stuff.

#define seq_before(x,y) ({typeof(x) _dummy = (x - y); \
                          _dummy > 1u << (7u + 8u * (sizeof(_dummy) - 1u));})
#define seq_after(x,y) ({typeof(x) _dummy = (y - x); \
                         _dummy >= 1u << (7u + 8u * (sizeof(_dummy) - 1u));})

Thanks for testing (I never did it :) ) and please test that one.

Best regards,
	Sven

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