Recognising that wc is a lexer problem and implementing it using re2c would be my first choice here. That'll be building a similar state machine to what is done

Recognising that wc is a lexer problem and implementing it using re2c would be my first choice here. That'll be building a similar state machine to what is done by hand here, especially since the hand rolled one is still byte at a time (the main drawback to re2c's generated output).