[RFH] A simple way to figure out the number of bits used by a long double

[Paolo Carlini]

Hi,

I'm trying to simplify somewhat code in the library hashing floating
point numbers, and I would find very useful a simple "recipe" giving the
total number of bits actually used by a long double: the basic issue is
that for formats like the 80-bit Intel, I can't just rely on sizeof,
because the last 6 bytes are unused. At the moment I'm trying to cook up
something fixing that count with LDBL_MANT_DIG, but maybe there is
something simpler, maybe using preprocessor builtins?!?

Thanks in advance for any help...
Paolo.