sub IEEE80toIEEE64 {
    my $ieee80 = shift;
    
    # reverse the byte order; this makes it look like an Intel 80-bit doohickey
    my $ieee80r = join('', reverse(split //, unpack 'a10', $ieee80));

    # now pick it apart
    my( $discard, $mantissa, $hidden, $exponent, $sign ) =
        unpack 'a11 a52 a1 a15 a1', unpack 'b80', $ieee80r;

    # readjust the exponent
    $exponent = unpack( 'v', pack 'b15', $exponent ) - 16383 + 1023;
    $exponent = 32767, $mantissa = '0' x 52
        if $exponent < 0 or $exponent > 2047;
    $exponent = unpack 'b11', pack 'v', $exponent;

    # put it back together
    my $ieee64r = join('', $mantissa, $exponent, $sign);

    # reverse the byte order back to Motorola-normal
    my $ieee64 = join('', reverse(split //, unpack 'a8', pack 'b64', $ieee64r));
    
    # ...and convert the binary to a Perl NV
    return unpack 'd', $ieee64;
}