docs: public static float entropy(int[] c) {
  		//total 频率总数
  		float total = sum(c);
  		if(total==0f)
  			return 0f;
  		float[] prop = new float[c.length];
  		for(int i=0;i<c.length;i++){
  			prop[i] = c[i]/(total);	
  		}
  		return entropy(prop);
  	}