Split a circular linked list in two halves in C

#include<stdio.h>
#include<stdlib.h>
struct Node
{
  int data;
  struct Node *next;
};

//function to split list into two halves
void splitList (struct Node *head, struct Node **head1, struct Node **head2)
{
  struct Node *slow = head;
  struct Node *fast = head;

  if (head == NULL)
    return;

  //finding middle of the list 
  while (fast->next != head && fast->next->next != head)
    {
      fast = fast->next->next;
      slow = slow->next;
    }

  if (fast->next->next == head)
    fast = fast->next;

  *head1 = head;

  if (head->next != head)
    *head2 = slow->next;

  fast->next = slow->next;

  slow->next = head;
}

void insertStart (struct Node **head, int data)
{
  struct Node *newNode = (struct Node *) malloc (sizeof (struct Node));
  newNode->data = data;

  // if its the first node being entered
  if (*head == NULL)
    {
      *head = newNode;
      (*head)->next = *head;
      return;
    }

  struct Node *curr = *head;

  // traverse till last node in LL
  while (curr->next != *head)
    {
      curr = curr->next;
    }

  curr->next = newNode;
  newNode->next = *head;
  *head = newNode;
}

void display (struct Node *head)
{
  // if there are no node in LL
  if (head == NULL)
    return;

  struct Node *temp = head;

  //need to take care of circular structure of LL
  do
    {
      printf ("%d ", temp->data);
      temp = temp->next;

    }
  while (temp != head);
  printf ("\n");
}

int main ()				//main function
{
  struct Node *head = NULL;
  struct Node *head1 = NULL;
  struct Node *head2 = NULL;

  insertStart (&head, 6);
  insertStart (&head, 5);
  insertStart (&head, 4);
  insertStart (&head, 3);
  insertStart (&head, 2);
  insertStart (&head, 1);

  printf ("Linked List is: ");
  display (head);

  splitList (head, &head1, &head2);

  printf ("\nFirst half data: ");
  display (head1);

  printf ("\nSecond half data: ");
  display (head2);
  return 0;
}