Program to compare performance of VTable versus Switch in a simple program

vtable-vs-switch.c

/* Compile with: gcc -O3 vtable-vs-switch.c -o vtable-vs-switch */
/* Execute: time ./vtable-vs-switch switch                      */
/*          time ./vtable-vs-switch vtable                      */
/* Execution time should last less than a minute.               */

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

static FILE *output;

/* Define some workers with equal prototypes */
void worker1(FILE *f)
{
	fprintf(f, "I'm worker 1\n");
}

void worker2(FILE *f)
{
	fprintf(f, "I'm worker 2\n");
}

void worker3(FILE *f)
{
	fprintf(f, "I'm worker 3\n");
}

void worker4(FILE *f)
{
	fprintf(f, "I'm worker 4\n");
}

enum worker_id {
	WORKER1 = 0,
	WORKER2,
	WORKER3,
	WORKER4,
	N_WORKERS,
};

/* These are for function pointer call */
typedef void (*worker)(FILE*);
worker vtable[] = {
	worker1,
	worker2,
	worker3,
	worker4,
};

void do_work_vtable(enum worker_id id)
{
	(vtable[id])(output);
}

/* These are for switch style call */
void do_work_switch(enum worker_id id)
{
	switch (id) {
		case WORKER1: worker1(output); break;
		case WORKER2: worker2(output); break;
		case WORKER3: worker3(output); break;
		case WORKER4: worker4(output); break;
	}
}

/* Lets benchmark */

void usage(const char *prog)
{
	fprintf(stderr, "Usage: %s (switch|vtable) [NUM_EXECUTIONS [OUTPUT]]\n", prog);
	exit(1);
}

int main(int argc, char *argv[])
{
	if (argc <= 1)
		usage(argv[0]);

	const char *method = argv[1];
	if (strcmp(method, "switch") != 0 && strcmp(method, "vtable") != 0)
		usage(argv[0]);

	int N = argc >= 3 ? atoi(argv[2]) : 1000000000;
	output = argc >= 4 ? fopen(argv[3], "w") : fopen("/dev/null", "w");

	printf("Running experiment:\n");
	printf("  Method: %s\n", method);
	printf("  Number of executions: %d\n", N);

	if (strcmp(method, "switch") == 0) {
		while (N--)
			do_work_switch(N % N_WORKERS);
	} else if (strcmp(method, "vtable") == 0) {
		while (N--)
			do_work_vtable(N % N_WORKERS);
	}

	return 0;
}