Finds the missing element in an array using xor

xor_finder.c

#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>

//#define DEBUG

#define POWER 8
#define MAX 256

void shuffle(int* array, size_t n) {
  if (n > 1) {
    size_t i;
    for (i = n - 1; i > 0; i--) {
      size_t j = (unsigned int)arc4random_uniform(i + 1);
      int t = array[j];
      array[j] = array[i];
      array[i] = t;
    }
  }
}

void print_array(int* array, size_t n, const char* message) {
  unsigned int i;

  printf("\n%s:\n", message);

  for (i = 0; i < n; ++i) {
    printf("%d ", array[i]);
  }

  printf("\n\n");
}

int main() {
  int i, xor_result, missing;
  int* array = malloc((sizeof(int) * MAX) - 1);
  int sum = (MAX * (MAX + 1)) / 2;
  int pos;

  struct timeval tv;
  gettimeofday(&tv, NULL);
  int usec = tv.tv_usec;
  srand48(usec);

  missing = arc4random_uniform((unsigned int)MAX);

  printf("missing number is %d\n", missing);

  xor_result = MAX;
  pos = 0;

  // initialize array
  for (i = 1; i <= MAX; ++i) {
    if (i == missing) {
      continue;
    }
    array[pos] = i;
    ++pos;
  }

#ifdef DEBUG
  print_array(array, MAX, "original array");
#endif

  shuffle(array, MAX);

#ifdef DEBUG
  print_array(array, MAX, "shuffled array");
#endif

  for (i = 0; i < MAX; ++i) {
    xor_result = xor_result ^ array[i];
  }

  printf("sum:        %d\n", sum);
  printf("xor_result: %d\n", xor_result);

  free(array);
}