Mark: 13 revision(s)

2008-11-03T05:18:42Z

13 revision(s)

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got trouble to login Linix.
Used window MVS to develop program.

http://www.cplusplus.com/reference/clibrary/ctime/clock.html

Some info about function "clock".

CLOCKS_PER_SEC specifies the relation between a clock tick and a second (clock ticks per second).

clock() return the current clock ticks but it is not a value of time.

clock_t is variable defined in <ctime>.

int main()
{
clock_t start_clock_t;
clock_t end_clock_t;
int n;
int a;
clock_t time_elapsed_t;
start_clock_t=clock();
for (n=0; n<100000000; n++)
{
}
end_clock_t=clock();
time_elapsed_t =(end_clock_t - start_clock_t);
printf ("%ld",time_elapsed_t);
return 0;
}

this is the code to test the clock ticks in the addition.
it is about 220.

When we add an addition in the for lop.
for (n=0; n<100000000; n++)
{
a++
}

clock ticks is not much different.

When we change the variable to double.

the clock ticks increase 4 times.

The mean time usage in the for loops is comparing n and the end loop condition.

i want the addition become a mean time usage in the for loop.
I try to decrease the comparing times.
#include <stdio.h>
#include <time.h>
int main()
{
clock_t start_clock_t;
clock_t end_clock_t;
int n;
int a;
clock_t time_elapsed_t;
start_clock_t=clock();
a=0;
for (n=0; n<10000000; n++)
{
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;

}
end_clock_t=clock();
time_elapsed_t =(end_clock_t - start_clock_t);
printf ("%ld",time_elapsed_t);
return 0;
}

the clock ticks decrease to about 188.
In second version,5 times more addition command had been done.

i guess the best way to test the time of addition is copy and paste 10000000 times "a++" in the main.c .
So pure machine code of addition can run for test.
And get the clock ticks number.

The for loops include the compare command which makes the time measurement difficult.
I think i can't get answer using for loops

SE250:lab-1:kkan048 - Revision history

Mark: 13 revision(s)