#ifdef GETTIMEOFDAY
#include <sys/time.h> // For struct timeval, gettimeofday
#else
#include <time.h> // For struct timespec, clock_gettime, CLOCK_MONOTONIC
#endif
#include <stdio.h>
#include <stdlib.h>

double wall_time() {
#ifdef GETTIMEOFDAY
  struct timeval t;
  gettimeofday(&t, NULL);
  return 1. * t.tv_sec + 1.e-6 * t.tv_usec;
#else
  struct timespec t;
  clock_gettime(CLOCK_MONOTONIC, &t);
  return 1. * t.tv_sec + 1.e-9 * t.tv_nsec;
#endif
}

void die(const char *message) {
  perror(message);
  exit(EXIT_FAILURE);
}