Messages in this thread | | | Date | Sat, 07 Jan 2006 10:21:06 +1100 | From | Peter Williams <> | Subject | Re: [PATCH] lib: Fix bug in int_sqrt() for 64 bit longs |
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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
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