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common-lispinfinity

representing infinity and NAN independent of implementation

Is there an implementation independent way of representing infinity or not a number (NAN) in Common Lisp? It would need to be a double float, and have both positive and negative values. In SBCL, the results of

(apropos "INFINITY")

include

SB-EXT:DOUBLE-FLOAT-NEGATIVE-INFINITY (bound)
SB-EXT:DOUBLE-FLOAT-POSITIVE-INFINITY (bound)

but I need it to be available in all implementations. I have an addendum to a package to write that runs on all platforms and it needs a representation of infinity and NAN. Even functions from another library would suffice.

I got iee-floats loaded and it's a part of my library now. I have a function that detects if a number is NaN and one that detects whether a number is infinity; I haven't tested NaN out but my infinity function needs the number to be a double-float. SBCL's SB-EXT:DOUBLE-FLOAT-POSITIVE-INFINITY works but I would need it to be implementation independent.

Solution

  • If you load GSLL (in quicklisp), you have gsl:+positive-infinity+, gsl:+negative-infinity+, and even gsl:+nan+. These should work anywhere that GSLL is installable.