anchor.diff:     Reg#(Bool) positive_reg <- mkReg(False);
      (* fire_when_enabled *)
      rule react;
  -      let new_count = cnt;
  -      if (inc_wire > dec_wire)
  -	 new_count = cnt + (inc_wire - dec_wire);
  -      else
  -	 new_count = cnt - (dec_wire - inc_wire);
  +      let new_count = (cnt + inc_wire) - dec_wire;
         cnt <= new_count;
         positive_reg <= (new_count > 0);
      endrule
  
positive.code:    method ActionValue#(Bool) maybeDecrement(UInt#(count_sz) x);
     method Action increment(UInt#(count_sz) x);
     method UInt#(count_sz) read();
     method Bool positive();
  endinterface
  
  
negative.code:       dec_wire <= x;
     endmethod
     method ActionValue#(Bool) maybeDecrement(UInt#(count_sz) x);
        if (cnt >= x) begin
  	 dec_wire <= x;
  	 return True;
        end
  