[Haskell] Platform-dependent behaviour with functions on NaN
lennart at augustsson.net
Fri Apr 14 10:04:51 EDT 2006
Yeah, I think it boils down to different representations of NaN on
different platform. I guess I forgot to test for NaN when I wrote
(the C code for) decodeFloat. It should generate some consistent
On the other hand, if you have code that possible divides by 0
and don't check for it, well...
It would be nice if Haskell allowed you to turn on signalling NaNs.
Geisler, Tim (EXT) wrote:
> In Haskell, the behaviour of functions on floating-point values which
> are NaN can be platform dependent.
> On "SunOS sun 5.9 Generic_118558-09 sun4u sparc SUNW,Sun-Blade-1500":
> Prelude> ceiling (0/0)
> On Windows:
> Prelude> ceiling (0/0)
> Both machines use the binary distributions of GHC 6.4.1.
> In our production code, this error (which is actually an error in our
> program) occured inside a quite complex expression which can be
> simplified to max 0 (ceiling (0/0)). On Windows, we did not recognize
> the error in the program, because the complex expression just returned
> 0. On Solaris, the complex expression returned this large number (which
> represents in the application "the number of CPUs needed in a certain
> device" ;-)
> We develop Haskell programs on Windows and run them in production on
> Sparc with Solaris. It seems that we have to run special regression
> tests testing for differences between Sparc Solaris and Windows.
> The Haskell 98
> report http://www.haskell.org/onlinereport/basic.html#sect6.4 states:
> "The results of exceptional conditions (such as overflow or underflow)
> on the fixed-precision numeric types are undefined; an implementation
> may choose error (/_|_/, semantically), a truncated value, or a special
> value such as infinity, indefinite, etc."
> There has been some discussion six years ago and nearly two years ago:
> Is there a chance to
> - properly define the behaviour of functions depending on the function
> properFraction for values like NaN, Infinity, ...?
> - get an implementation of this in GHC which computes the same results
> for all platforms?
> Perhaps the function properFraction could raise an exception in case of
> isNaN and isInfinity?
> Other languages are more portable. E.g., for Java, these cases are
> http://java.sun.com/docs/books/jls/second_edition/html/typesValues.doc.html#9249 states:
> "All numeric operations with NaN as an operand produce NaN as a result."
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