segfault/massive memory use when using Data.Bits.shiftL
Hi, The following either eats memory until killed or segfaults (I can't pin down a reason for the difference). Tested with GHC 6.2.2 and 6.4.20050212, with various different libgmp3s under various Redhat and Debian platforms, and WinXP. Prelude :m +Data.Bits Prelude Data.Bits 18446658724119492593 `shiftL` (-3586885994363551744) :: Integer Cheers, Ganesh ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: segfault/massive memory use when using Data.Bits.shiftL
On Mon, Feb 28, 2005 at 02:55:56PM +, Ganesh Sittampalam wrote: Hi, The following either eats memory until killed or segfaults (I can't pin down a reason for the difference). Tested with GHC 6.2.2 and 6.4.20050212, with various different libgmp3s under various Redhat and Debian platforms, and WinXP. Prelude :m +Data.Bits Prelude Data.Bits 18446658724119492593 `shiftL` (-3586885994363551744) :: Integer Cheers, Ganesh shiftL for Integer is defined in fptools/libraries/base/Data/Bits.hs: class Num a = Bits a where shiftL :: a - Int - a x `shiftL` i = x `shift` i instance Bits Integer where shift x i | i = 0= x * 2^i | otherwise = x `div` 2^(-i) IOW, for y 0: x `shiftL` y = x `shift` y = x `div` 2^(-y) and calculating, in your case, 2^3586885994363551744 is not something your computer is going to like... as it's probably a number which doesn't fit in our universe :) Still, a segfault might point at a bug, which I unfortunately won't be able to say much about. (Due to lack of knowledge information.) Greetings, Remi -- Nobody can be exactly like me. Even I have trouble doing it. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: segfault/massive memory use when using Data.Bits.shiftL
On Mon, 28 Feb 2005, Remi Turk wrote: On Mon, Feb 28, 2005 at 02:55:56PM +, Ganesh Sittampalam wrote: Prelude :m +Data.Bits Prelude Data.Bits 18446658724119492593 `shiftL` (-3586885994363551744) :: Integer and calculating, in your case, 2^3586885994363551744 is not something your computer is going to like... as it's probably a number which doesn't fit in our universe :) Hmm, good point. I hadn't thought about the fact that the number of digits in the answer would be rather large... Still, a segfault might point at a bug, which I unfortunately won't be able to say much about. (Due to lack of knowledge information.) My googling suggests that gmp is prone to segfaulting when things get too large for it, so I'll just chalk it up to that. I apologise for thinking this was a bug :-) Cheers, Ganesh ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: segfault/massive memory use when using Data.Bits.shiftL
On Mon, Feb 28, 2005 at 10:59:32PM +, Ganesh Sittampalam wrote: On Mon, 28 Feb 2005, Remi Turk wrote: On Mon, Feb 28, 2005 at 02:55:56PM +, Ganesh Sittampalam wrote: Prelude :m +Data.Bits Prelude Data.Bits 18446658724119492593 `shiftL` (-3586885994363551744) :: Integer and calculating, in your case, 2^3586885994363551744 is not something your computer is going to like... as it's probably a number which doesn't fit in our universe :) Hmm, good point. I hadn't thought about the fact that the number of digits in the answer would be rather large... Actually, the final answer will be 0: It's only the intermediate value that gets ridiculously large. Still, a segfault might point at a bug, which I unfortunately won't be able to say much about. (Due to lack of knowledge information.) My googling suggests that gmp is prone to segfaulting when things get too large for it, so I'll just chalk it up to that. I apologise for thinking this was a bug :-) No need to apologize. Segfaults _are_ IMHO almost always bugs. And in this case too, though the fault isn't GHCs. Groeten, Remi Cheers, Ganesh -- Nobody can be exactly like me. Even I have trouble doing it. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
