Red Hat Bugzilla – Bug 873385
Random module fails on Doubles because of odd minBound behaviour
Last modified: 2015-12-02 11:03:41 EST
I'm not sure how live this project is any more, but here goes... $ rpm -q hugs98 hugs98-2006.09-11.fc17.x86_64 $ hugs Type :? for help Hugs> :load Random Random> randomR (1::Double,10) (mkStdGen 3) ( Program error: arithmetic overflow The equivalent answer in ghci is: (1.928919588914141,2109513658 1655838864) This seems to happen because: Random> minBound::Int -2147483648 Random> toInteger (minBound::Int) -18446744071562067968 Random> toInteger (maxBound::Int) 2147483647 The implementation of Random on Doubles uses the construction "toInteger (minBound::Int)" to get an integer random number, but the implementation of Random on integers falls over on values greater than 2^32-1.
Ah I see. I wonder if it is a 64 bit issue? Unfortunately hugs is pretty much dead^Wunmaintained now AFAIK. Anyway I will try to have a look at the code later and maybe compare with the current random package and see if I can come up with a patch... of course there could be other 64bit problems lurking.
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Still happening with F19
And still for F21 of course. hugs98.i686 seems okay: so installed that by hand would be a workaround perhaps. I tested on Ubuntu amd64 and got the same error (I guess the Debian package also has this problem).
(FWIW 64bit ghci gives: Prelude> toInteger (minBound :: Int) -9223372036854775808 ) Hugs seems to be assuming Int32, but something is indeed going wildly wrong with "toInteger (minBound::Int)". I looked at: src/bignums.c:326:primFun(primIntToInteger) { /* Conversion :: Int -> Integer */ but I am not familiar with hugs' internals and things seems to get into deep water quickly. BTW "toInteger (minBound + 1:: Int) -1" and "toInteger (minBound -1:: Int) +1" seem to give the expected answer. I almost wonder if it would be better to drop 64bit arch build for hugs.
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