Grammar re;
Lexer

        notst = Any - '*';
        notstsl = notst - '/';

        com1 = '/*' (notst | '*'+ notstsl)* '*'+ '/';
        com2 = '/*' notst* ('*' (notstsl notst*)?)* '*/'; //alt1 //alt2 //alt3 //alt4
        //alt1 com2 = Shortest ('/*' Any* '*/');
        //alt2 com2 = '/*' (Any* - '*/') '*/';
        //alt3 com2 = '/*' (('' Lookahead Not '*/') Any)* '*/';
        //alt4 com2 = '/*' (Any* Except (Any* '*/' Any*)) '*/';

        dummy = notst | notstsl;

Parser

p = com1 | com2 | dummy;