Execution time in nano seconds and related issues
- by anup
Hi All,
I am using the following code to compute execution time in milli-secs.
struct timespec tp;
if (clock_gettime (CLOCK_REALTIME, &tp) == 0)
return ((tp.tv_sec * 1000000000) + tp.tv_nsec);
else
return ;
Can you please tell me whether this is correct?
Let's name this function comptime_nano().
Now, I write the following code in main() to check execution times of following operations.
unsigned long int a, b, s1, s3;
a = (unsigned long int)(1) << 63;
b = (unsigned long int)(1) << 63;
btime = comptime_nano();
s1 = b >> 30;
atime = comptime_nano();
printf ("Time =%ld for %lu\n", (atime - btime), s1);
btime = comptime_nano();
s3 = a >> 1;
atime = comptime_nano();
printf ("Time =%ld for %lu\n", (atime - btime), s3);
To my surprise, the first operation takes about roughly 4 times more time than the second. Again, if I change the relative ordering of these operations, the respective timings change drastically.
Please comment...
