23 Aug
2007
23 Aug
'07
8:32 a.m.
On Thu, 23 Aug 2007, Neil Mitchell wrote:
Hi
Its (==) isn't reflexive (is it transitive? probably, at least if there aren't too many optimizations, but floating-point transitive equality isn't very useful).
It's not even referentially transparent in all cases. a == b may fail while the double's are in the high precision registers, and then succeed later on in the program once they are truncated. I think you have to specify -fexcess-precision with GHC to get this behaviour.
That's really bad. This will invalidate the clever algorithms for computing (+) and (*) with doubled precision (EFT - error free transformations). http://66.102.9.104/search?q=cache:8vni-CqtINkJ:www.ti3.tu-harburg.de/paper/rump/Ru05c.pdf+TwoSum&hl=de&ct=clnk&cd=1&gl=de