sub fix_endian {
    my $h = shift;
    my $h = reverse $h;
    $h =~ s/(.)(.)/$2$1/g;  # only required if using 'H' not 'h' template
    return $h;
}
sub hex2int   { unpack("N", pack("H8", substr('0'x8 .$_[0], -8))) }
sub hex2float { unpack("f", pack("H8", substr('0'x8 .$_[0], -8))) }
sub hex2double{ unpack("d", pack("H16", substr('0'x16 .$_[0], -16))) }

while(<DATA>){
    s/\s+//g;
    next unless $_;
    $, = "\t";
    print $_, hex2int($_), hex2float($_), hex2double($_), hex2double(fix_endian($_)), "\n";
}

__DATA__
0000 0034 
0000 31b1
01
91
403b 8811 bb13 66e4