code: function(key,piece){
  		var bd = this.board;
  		if(piece.isnull){ return -1;}
  
  		key &= 0x0F;
  		if     (key===this.UP){ return piece.by;}
  		else if(key===this.DN){ return 2*bd.rows-piece.by;}
  		else if(key===this.LT){ return piece.bx;}
  		else if(key===this.RT){ return 2*bd.cols-piece.bx;}
  		return -1;
  	}
docs: --------------------------------------------------------------------------- bd.exec.distObj()      上下左右いずれかの外枠との距離を求める ---------------------------------------------------------------------------