nanosleep纳秒级延迟

//函数原型 int nanosleep(struct timespec *req, struct timespec *rem)
//参数列表：
//  req:要求的睡眠时间
//  rem:剩余的睡眠时间
//返回值：
//  0：成功；-1，失败，errno保存错误代码

//目的：纳秒级别的延迟
int nano_delay(long delay)
{
    struct timespec req, rem;
    long nano_delay = delay;
    int ret = 0;
    while(nano_delay > 0)
    {
            rem.tv_sec = 0;
            rem.tv_nsec = 0;
            req.tv_sec = 0;
            req.tv_nsec = nano_delay;
            if(ret = (nanosleep(&req, &rem) == -1))
            {
                printf("nanosleep failed.
");                
            }
            nano_delay = rem.tv_nsec;
    };
    return ret;
}

//测试，纳秒级延迟的误差率
int main()
{
    int ret = 0;
    long delay = 0;
    struct timespec start, end, interv;
    for(delay = 1000; delay < 1000*1000; delay+=1000)
    {   
        curr_time(&start);
        nano_delay(delay);
        curr_time(&end);
        diff(&start, &end, &interv);
        printf("delay = %ld, real delay = %ld, error = %g.
", delay, interv.tv_sec * 1000000000 + interv.tv_nsec, (float)(interv.tv_sec * 1000000000 + interv.tv_nsec - delay)/delay );
    }

}

//测试结果：
//  Duo CPU e8200
//  Ubuntu 12.10 Kernel 3.4
//