jiffies overflow

strongzgy

在编写驱动是不能直接用如下的方法判断是否时间到的：
unsigned long timeout = jiffies + HZ/2;
if(timeout
int main(void)
{
        char i = -10;
        char j = -20;
        char k = 4;
        unsigned char time1 = 256;
        unsigned char time2 = 234;
        printf("i is: 0x%x, j is: 0x%x, k is: 0x%x, -1 is: 0x%x, -0 is: 0x%x\n",
                (unsigned char)i, (unsigned char)j, (unsigned char)k, (unsigned char)-1, (unsigned char)-0);
        printf("(char)time1 -(char)time2 is: %d\n", (char)time1 - (char)time2);
        printf("time1 - time2 is: %d\n", time1 - time2);
        return 0;
}
这段函数运行结果是：
i is: 0xf6, j is: 0xec, k is: 0x4, -1 is: 0xff, -0 is: 0x0
(char)time1 -(char)time2 is: 22
time1 - time2 is: -234
可以看出， time_before time_after巧妙的利用了负数的补码表示


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