Bug in C++ interface (comparison between rational and double)
marc.glisse at normalesup.org
Wed Jan 28 09:24:11 CET 2009
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:
> 1) add support for comparison between mpq and double in C interface and
> use that in gmpxx.h
> 2) add infinity (and nan) check in comparison eval specializations in
> 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
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)
PS: anybody notice on the gmplib webpage that the server migration should
be complete in 9 months?
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