On Tue, 27 Jan 2009, Abramo Bagnara wrote:
The comparison between mpz_class and double works fine with +inf and -inf, while the comparison between mpq_class and double gives a floating point exception, due to inappropriate mpq_set_d call in eval specialization.
I see two way to fix this:
- add support for comparison between mpq and double in C interface and
use that in gmpxx.h
- add infinity (and nan) check in comparison eval specializations in
gmpxx.h
IMHO 1) gives a more complete solution. If you want we're willing to write the (trivial) patch.
Some advantages of solution 2 (I am not saying I am in favor of 2, just mentionning them for completeness) are that the patch is small (if(isfinite(d)) current code; else return 0<d;), does not introduce any new interface, and has absolutely no impact on the code when compiled with g++ -ffinite-math-only.
It looks like comparison is the only operation where a Inf or NaN double makes sense in gmpxx (all the others return a gmp type, which can not represent Inf or NaN) (actually division by Inf could make sense too).
Just curious: what application do you have where it is useful to compare a gmp type to a non-finite double? (I am not questionning the usefulness of the feature request but genuinely interested)