Here's a different approach specifically for the 4-element dotted form:

  (eval$_)=~/^[\0-\xff]{4}\z/
[download]

This requires perl-5.6.0 or later; extending it for the other forms becomes rather uglier:

  (eval"0.0.$_")=~/^\0\0(.|[\0-\xff]([\0-\x{ffffff}]|[\0-\xff]([\0-\x{
+ffff}]|[\0-\xff]{2})))\z/s
[download]

Of course the usual caveats about eval apply, but this is golf ...

Hugo