sub fmt{
    my $bin = unpack 'Q', pack 'd', $_[0];
    my $sign = ( $bin & 0x8000000000000000 );
    my $exp  = ( $bin & 0x7FF0000000000000 ) >> 52; $exp -= 1023;
    my $mant = ( $bin & 0x000FFFFFFFFFFFFF );
    sprintf "%s0x1.%xp%d", ( $sign ? '-' : '' ), $mant, $exp;
}