sub double_from_hex { unpack 'd', scalar reverse pack 'H*', $_[0] }

use constant POS_INF => double_from_hex '7FF0000000000000';
use constant NEG_INF => double_from_hex 'FFF0000000000000';

use constant qNaN    => double_from_hex '7FF8000000000000';
use constant NaN     => qNaN;

print(POS_INF, "\n");  # 1.#INF
print(NEG_INF, "\n");  # -1.#INF
print(qNaN,    "\n");  # 1.#QNAN