#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <stdint.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <sys/time.h>

struct event {
  uintptr_t addr;
  int nb_access;
} __attribute__((packed));

int fd;
int n;
struct event* events;
int (*nb_access_at)(int n) = NULL;

double timestamp() {
  struct timeval tv;
  gettimeofday(&tv, NULL);
  return tv.tv_sec + 1e-6*tv.tv_usec;
}

int nb_access_at_mmap(int n) {
  return events[n].nb_access;
}

int nb_access_at_read(int n) {
  struct event tmp;

  lseek(fd, n * sizeof(tmp), SEEK_SET);
  
  if(read(fd, &tmp, sizeof(tmp)) == -1) {
    fprintf(stderr, "read(): %s\n", strerror(errno));
    exit(2);
  }

  return tmp.nb_access;
}

void usage(const char* self) {
  fprintf(stderr, "Usage: %s filename [mmap or read]\n", self);
  exit(1);
}

int main(int argc, char** argv) {
  if(argc != 3)
    usage(argv[0]);

  if(strcmp(argv[2], "mmap") == 0)
    nb_access_at = nb_access_at_mmap;
  else if(strcmp(argv[2], "read") == 0)
    nb_access_at = nb_access_at_read;
  else
    usage(argv[0]);
  
  fd = open(argv[1], O_RDONLY);

  if(fd == -1) {
    fprintf(stderr, "open(%s): %s\n", argv[1], strerror(errno));
    exit(2);
  }
  
  struct stat st;
  fstat(fd, &st);

  n = st.st_size / sizeof(struct event);

  printf("The trace file contains %d events\n", n);

  events = mmap(NULL, st.st_size, PROT_READ, MAP_SHARED, fd, 0);

  if(events == MAP_FAILED) {
    fprintf(stderr, "mmap(): %s\n", strerror(errno));
    exit(2);
  }
  
  double start = timestamp();
  int total = 0;
  for(int i=0; i<n; i++)
    total += nb_access_at(i);
  double end = timestamp();
  
  printf("Average access per memory address: %lf\n", total/(double)n);
  printf("Elasped time: %lf\n", end - start);
  
  return 0;
}