Re: [PATCH] lib: Fix bug in int_sqrt() for 64 bit longs

[Peter Williams <pwil3058@bigpond.net.au>]

Eric Dumazet wrote:
> Peter Williams a écrit :
>
> > The implementation of int_sqrt() assumes that longs have 32 bits.  On 
> > systems that have 64 bit longs this will result in gross errors when 
> > the argument to the function is greater than 2^32 - 1 on such systems. 
> > I doubt whether any such use is currently made of int_sqrt() but the 
> > attached patch fixes the problem anyway.
> >
> > Signed-off-by: Peter Williams <pwil3058@bigpond.com.au>
> >
> >
> > ------------------------------------------------------------------------
> >
> > Index: GIT-warnings/lib/int_sqrt.c
> > ===================================================================
> > --- GIT-warnings.orig/lib/int_sqrt.c    2005-10-25 13:55:22.000000000 
> > +1000
> > +++ GIT-warnings/lib/int_sqrt.c    2006-01-06 14:29:19.000000000 +1100
> > @@ -15,7 +15,7 @@ unsigned long int_sqrt(unsigned long x)
> >      op = x;
> >      res = 0;
> >  
> > -    one = 1 << 30;
> > +    one = 1 << (BITS_PER_LONG - 2);
> >      while (one > op)
> >          one >>= 2;
> >  
>
>
> Are you sure it works ?
>
> I would have writen :
>
> one = 1L << (BITS_PER_LONG - 2);

I think you're right as just using 1 would make the expression an 
integer variable and the compiler would complain about shifting too far 
unless integers were the same size as longs.  (I don't have a 64 bit 
system to confirm that on which is why it snuck by me. :-()

Thanks
Peter
--
Peter Williams                                   pwil3058@bigpond.net.au

"Learning, n. The kind of ignorance distinguishing the studious."
 -- Ambrose Bierce
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