https://www.cnblogs.com/asmblog/archive/2013/05/07/3063809.html
https://www.zhihu.com/question/21471960
http://blog.csdn.net/hanchaobiao/article/details/73150405
https://www.cnblogs.com/hqutcy/p/7248506.html
https://www.cnblogs.com/greenteemo/p/6745404.html
