关于<<= 的意义求解

关于<<= 的意思求解？

C/C++ code

int connect_retry(int sockfd,const struct sockaddr * addr,socklen_t alen){    int nsec;     printf("connecting\n");    for(nsec = 1; nsec <= MAXSLEEP; nsec<<=1)    {        if(connect(sockfd,addr,alen) == 0)        {            printf("connected\n");            return 0;        }// if        if(nsec <= MAXSLEEP/2)//    delay            sleep(nsec);    }// for:    return 0;}