For days I'm fighting against a weird bug.
My Haskell code calls into a C function residing in a DLL (I'm on Windows,
the DLL is generated using Visual Studio). This C function computes a
floating point expression. However, the floating point result is incorrect.
I think I found the source of the
Interesting. This could be the cause of a weird floating point bug
that has been showing up in the ghc testsuite recently, specifically
affecting MacOS/Intel (but not MacOS/ppc).
http://darcs.haskell.org/testsuite/tests/ghc-regress/lib/Numeric/num009.hs
That test compares the result of
Well this situation can indeed not occur on PowerPCs since these CPUs just
have floating point registers, not some weird dual stack sometimes /
registers sometimes architecture.
But in my case the bug is consistent, not from time to time.
So I'll try to reduce this to a small reproducible test
What floating point model is your DLL compiled with? There are a variety of
different options here with regards to optimizations, and I don't know about
the specific assembly that each option produces, but I know there are
options like Strict, Fast, or Precise, and maybe when you do something
I tried both precise and fast, but that did not help. Compiling to SSE2
fixed it, since that does not use a floating point stack I guess.
I'm preparing a repro test case, but it is tricky since removing code tends
to change the optimizations and then the bug does not occur.
Does anybody know what
On Fri, Apr 03, 2009 at 10:10:17PM +0200, Peter Verswyvelen wrote:
I tried both precise and fast, but that did not help. Compiling to SSE2
fixed it, since that does not use a floating point stack I guess.
You didn't say what version of GHC you are using, but it sounds like
this might already be
Ouch, what a waste of time on my side :-(
This bugfix is not mentioned in the notable bug fixes
herehttp://haskell.org/ghc/docs/6.10.2/html/users_guide/release-6-10-2.html
Since this is such a severe bug, I would recommend listing it :)
Anyway, I have a very small repro test case now. Will
Okay, I can confirm the bug is fixed.
It's insane this bug did not cause any more problems. Every call into every
C function that uses floating point could have been affected (OpenGL, BLAS,
etc)
On Fri, Apr 3, 2009 at 10:47 PM, Peter Verswyvelen bugf...@gmail.comwrote:
Ouch, what a waste of
