Lexer in D

[Namespace]

I never used the -profile flag before (only -conv) so I want to 
ask if I understand it right:
http://dpaste.1azy.net/4382097b
It seems that the call which is listed on line 133

1589328      214949      214948           0     pure @trusted 
dchar std.utf.decode!(const(immutable(char)[])).decode(ref 
const(immutable(char)[]), ref uint)

take the most time/performance. Am I right?
And why is something decoded? Should I use dchar instead of char?

And I do not take anything that is already finished, because I 
want to be more familiar with the matter.
I want to see, what you have to note in order to get performance.
The 24 msecs would obviously be a dream, but I would be pleased 
with 50-100 msecs. :D