printf "%.20g\n", unpack 'd', scalar reverse pack 'NN', 0x7fefffff, 0xffffffff;;
1.7976931348623157e+308

printf "%.20g\n", unpack 'd', scalar reverse pack 'NN', 0x7fffffff, 0xffffffff;;
1.#QNAN

printf "%.20g\n", unpack 'd', scalar reverse pack 'NN', 0xffefffff, 0xffffffff;;
-1.7976931348623157e+308

printf "%.20g\n", unpack 'd', scalar reverse pack 'NN', 0xffffffff, 0xffffffff;;
-1.#QNAN