Include longdblkind in perl -V output.
perldelta for b5b6210a9/#46947
hexfp: scan_num also handles hexadecimal floats now.
hexfp: Likely changes for double-double tests.

(from sisyphus, but unverified.)
hexfp: Modify the exponent explicitly in each branch.
hexfp: double-double needs extracting the low lead nybble.