[Haskell-cafe] ghc 6.8.1 bug?

SevenThunders mattcbro at earthlink.net
Fri Nov 16 10:09:01 EST 2007

Simon Peyton-Jones wrote:
> Alberto, SevenThunders, Joel,
> Glark. This is not good. Thank you for being so polite about it.  And
> thanks for working on a reproducible test case -- without that we are 100%
> stuck.
> We did fix one just-possibly-related bug in 6.8 recently, which concerned
> the use of {-# UNPACK #-} on strict Double-sized fields in fixed,
> top-level data structures. I think it was only wrong on a 64-bit machine.
> http://www.haskell.org/pipermail/glasgow-haskell-users/2007-November/013454.html
> What is the word size on your machine?
> But that may well be a complete red herring.  We'll stand by.
> Simon

Well I am running windows xp-64 and I have an athlon x2.  Does a 64 bit ghc
exist for windows?  I just installed ghc 6.8.1 using the binary installer. 
I know the C code I link to is 32 bit.  I actually did have some problems
upgrading atlas some time ago, but that was a build failure.  I think I've
built atlas 3.7.11 and had trouble  installing 3.7.24.  I haven't bothered
to upgrade to 3.8, but I suppose I should get around to doing so.  Since my
current version of atlas passes the tests and has been working flawlessly
until the upgrade to ghc 6.8.1,   I'm not inclined to suspect that right

As for narrowing down a test case.  It's still a work in progress.  So far
it appears that I need to do a lot of computations before I see it.  Also
one oddity is that in that code that I have right now  I have to apply the
round function in my main routine to an arbitrary double, that's not even
used in the final calculation (but is printed), in order to see the spurious
NaNs.  I'm not sure if that means anything since the behavior is reminiscent
of buggy C code.  However my C code has already been through some valgrind
checks and some other tests.  I'm quite confident there are no memory faults
there.  If I save off my matrices right before doing the multiply the bug
goes away as well.

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