On 05/06/2017 06:00 PM, Andrew Parsloe wrote:
> I have finally got to grips with l3fp's exception handling. (The main
> difficulty was realising that an exception like division_by_zero is a
> different creature from the flag fp_division_by_zero.) However, I was
> surprised to find that \fp_eval:n { ln(1) } raises the underflow flag:
> \flag_height:n { fp_underflow } displays 1.
> Andrew

Thanks for reporting.  This is a bug.  Somewhat known to me at least at
some point since I wrote in the source the following comment

%^^A todo: ln(1) should be "exact zero", not "underflow"

I need to revisit l3fp soonish, but sadly a realistic estimate of when
that'll be fixed is 1 year.  I've opened issue #364