#include <stdio.h>
#include <time.h>
#define CACHE_MIN (1024) /* smallest cache */
#define CACHE_MAX (1024*1024)
#define SAMPLE 10

int x[CACHE_MAX];

double get_seconds() { /* routine to read time */
	clock_t t;
    t = clock();
	return (double) t/ (double) CLOCKS_PER_SEC;
}

void main()
{
	int register i, index, stride, limit, temp;
	int steps, tsteps, csize;
	double sec0, sec; /* timing variables. */

	for (csize = CACHE_MIN; csize <= CACHE_MAX; csize = csize * 2)
		for (stride = 1; stride <= csize/2; stride = stride * 2) {
			sec = 0; /* initialize timer */
			limit = csize - stride + 1; /* cache size this loop */

			steps = 0;
			do { /* repeat until collect 1 second */
			   sec0 = get_seconds(); /* start timer */
			   for (i = SAMPLE * stride; i != 0; i = i - 1) /* larger sample */
			       for (index = 0; index < limit; index = index + stride)
				       x[index] = x[index] + 1; /* cache access */
			   steps = steps + 1; /* count while loop iterations */
			   sec = sec + (get_seconds() - sec0); /* end timer */
			} while (sec < 1.0); /* until collect 1 second */

			/* repeat empty loop to subtract loop overhead */
			tsteps = 0; /* used to match no. while iterations */
			do { /* repeat until same no. of iterations as above */
			   sec0 = get_seconds(); /* start timer */
			   for (i = SAMPLE * stride; i != 0; i = i - 1) /* larger sample */
			       for (index = 0; index < limit; index = index + stride)
				       temp = temp + index; /* dummy code */
			   tsteps = tsteps + 1; /* count while loop iterations */
			   sec = sec - (get_seconds() - sec0); /* - overhead */
			} while (tsteps < steps); /* until = no. iterations */

			printf("Size:%7d Stride:%7d read+write:%140.f ns\n",
				    csize * sizeof(int), stride * sizeof(int), 
					(double) sec*1e9/(steps*SAMPLE*stride*((limit-1)/stride+1)));
		}; /* endof both outer for loops */
}