test vectors from crlibm
http://lipforge.ens-lyon.fr/www/crlibm/
(the only modification was printf '\n' >>log2.testdata)

format:
	first line: func
	comment: #.*
	test record: round in out

round
	RN or N = to nearest
	RZ or Z = to zero
	RU or P = to +inf (up)
	RD or M = to -inf (down)

in:
out:
	2 32bit hex words