Implementation of merge sort on array of integers in C

merge_sort.c

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

int * merge_sort(int *parr, int arr_len);

void print_array(int *arr, int len_arr);

int main(void)
{
   int items[]   = { 5, 2, 7, 4, 1, 6, 3, 0 };
   int len_items = sizeof(items) / sizeof(*items);

   // Print original order
   print_array(items, len_items);

   // Merge sort
   merge_sort(items, len_items);

   // Print sorted order
   print_array(items, len_items);

   return EXIT_SUCCESS;
}


int * merge_sort(int *parr, int arr_len)
{
   if (arr_len == 1)
   {
      return parr;
   }

   /* Split array into two half-arrays */

   // Lengths of each half-array
   int left_len  = arr_len / 2;
   int right_len = arr_len - left_len;

   // Pointers to first index in each half-array
   int *pleft  = parr;
   int *pright = parr + left_len;

   /* Sort each half-array */

   int *left  = merge_sort(pleft, left_len);
   int *right = merge_sort(pright, right_len);

   /* Merge the two half-arrays */

   // Use "shelf" array to merge
   int *shelf_arr = (int *)malloc(arr_len * sizeof(int));

   // Merge
   int is_end_of_left  = 0;
   int is_end_of_right = 0;
   int *end_of_left    = left + left_len;
   int *end_of_right   = right + right_len;
   for (int i = 0; i < arr_len; ++i)
   {
      if (!is_end_of_left && !is_end_of_right)
      {
         if (*left < *right)
         {
            shelf_arr[i] = *left;
            ++left;
         }

         else
         {
            shelf_arr[i] = *right;
            ++right;
         }
      }
      else if (is_end_of_left && !is_end_of_right)
      {
         shelf_arr[i] = *right;
         ++right;
      }
      else
      {
         shelf_arr[i] = *left;
         ++left;
      }

      is_end_of_left  = (left < end_of_left) ? 0 : 1;
      is_end_of_right = (right < end_of_right) ? 0 : 1;
   }

   // Copy from "shelf" array into original array
   memcpy(parr, shelf_arr, arr_len * sizeof(int));

   free(shelf_arr);

   return parr;
}


void print_array(int *arr, int len_arr)
{
   for (int i = 0; i < len_arr; ++i)
   {
      printf("%d ", arr[i]);
      if (len_arr - 1 == i)
      {
         printf("\n");
      }
   }
}