/* gcc -W -Wall -O2 -o port80 port80.c */

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

#include <sys/io.h>

#define LOOPS 10000

inline unsigned long long rdtsc(void)
{
	unsigned long long tsc;

	asm volatile ("rdtsc": "=A" (tsc));

	return tsc;
}

inline void serialize(void)
{
	asm volatile ("cpuid": : : "eax", "ebx", "ecx", "edx");
}

int main(void)
{
	unsigned long long start;
	unsigned long long overhead; 
	unsigned long long output;
	unsigned long long input;
	int i;

	if (iopl(3) < 0) {
		perror("iopl");
		return EXIT_FAILURE;
	}

	asm volatile ("cli");
	start = rdtsc();
	for (i = 0; i < LOOPS; i++) {
	 	serialize();	
		serialize();
	}
	overhead = rdtsc() - start;

	start = rdtsc() + overhead;
	for (i = 0; i < LOOPS; i++) {
		serialize();
		asm volatile ("outb %al, $0x80");
		serialize();
	}
	output = rdtsc() - start;

	start = rdtsc() + overhead;
	for (i = 0; i < LOOPS; i++) {
		serialize();
		asm volatile ("inb $0x80, %%al": : : "al");
		serialize();
	}
	input = rdtsc() - start;
	asm volatile ("sti");

	output /= LOOPS;
	input  /= LOOPS;
	printf("cycles: out %llu, in %llu\n", output, input);

	return EXIT_SUCCESS;
}