for my $a (-2..10, 0.2, -0.2, 1 + 0.25e-15) {  
        $_ = unpack("b*", pack("d", $a));   # double to bit-pattern 
        s/(.{8})/$1 /g; tr[0][.];           # grouping&fmt.
        $_ = reverse $_;                    # formatting
        s/^(..)(.{12})(.*)/Sgn:$1  Exp: $2  Mant:(1,)$3/; 
        print "$a\t -- $_\n";
}