/**
 * Example of the use of 3 different ways of timing a function
 * The function should be fairly long running (say 0.5 sec) to get
 * reasonably reliable results
 * 
 * @author gtowell
 * Created: Sep 2020
 * **/

#include <time.h>
#include<stdio.h>

#define MSEC_MULT 1000000
#include <sys/time.h> //for gettimeofday

#include<sys/times.h>
#include <sys/resource.h> 

#define COLUM "%10.6f"

#ifndef NULL
#define NULL (void *) 0
#endif

/**
 * A silly function that just takes a while to complete.  
 * This is the thing to be timed
 * **/
void work()
{
    //Work to be timed
    for (int ii=0; ii<20; ii++)
    {
	for (int i=0; i<10000000; i++)
	{
	    int j=i*i;
	}
    }
    // end work
}

/**
 * Timing method 1
 * Uses the clock function from time.h
 * Probably the simplest to use, but maybe, arguably the least accurate
 * **/
void t1()
{
    clock_t start, end;
    start = clock();
    work();
    end = clock();
    float cpu_time_used = ((float) (end - start)) / CLOCKS_PER_SEC;
    printf(COLUM, cpu_time_used );
}
/**
 * Timing method 2.
 * **/
void t2()
{
    struct timeval begin, end;
    gettimeofday(&begin, NULL);
    work();
    gettimeofday(&end, NULL);
    float interval=(float)(end.tv_sec*MSEC_MULT+end.tv_usec - begin.tv_sec*MSEC_MULT-begin.tv_usec); 
    printf(COLUM, (interval/MSEC_MULT) );
}

/**
 * Utility function for t4
 * pulls the time out of a buffer
 * **/
double t2d(struct rusage buf)
{
    return (double)(buf.ru_utime.tv_sec + (double) buf.ru_utime.tv_usec / (double) CLOCKS_PER_SEC); 
}

/** 
 * final timing method
 * Yet another way of doing the same thing
 * Perhaps the most accurate, perhaps.
 * **/
void t4()
{
    struct rusage buf; 
    getrusage(RUSAGE_SELF, &buf);
    double startt=t2d(buf);
    work();
    getrusage(RUSAGE_SELF, &buf);
    double endt = t2d(buf);
    printf(COLUM, (endt-startt));
}

int main(void)
{
    printf("%10s%10s%10s\n", "T1", "T2", "T4");
    for (int i = 0; i < 5; i++)
    {
	t1();
	t2();
	t4();
    printf("\n");
    }
}