STM32 ------ 处理 int64 类型数据需要注意

uint64_t destime, oritime, rectime, tratime;
int64_t result;

result = ((rectime-oritime) + (tratime-destime))/2;

当((rectime-oritime) + (tratime-destime))是负数的时候，result不能得到正确的数，需要写成如下：

uint64_t destime, oritime, rectime, tratime;
int64_t result, tmp;

tmp = ((rectime-oritime) + (tratime-destime));
result = tmp/2;