Doubly-linked list with a single word per node

xlist.c

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

/* on Mac OS X sizeof(int) < sizeof(int *) so make sure we use a large enough integer! */
typedef int64_t integer_t;

typedef struct {
	int value;
	integer_t nextprev;
} node_t;

/* allocate and initialize a new node */
node_t *new_node(int value)
{
	node_t *n = malloc(sizeof(node_t));
	assert(n != NULL);
	n->value = value;
	n->nextprev = 0;
	return n;
}

/* insert node at the head of the list and return the new head */
node_t *insert_at_head(node_t *head, node_t *n)
{
	if (head == NULL) {
		n->nextprev = 0;
	} else {
		n->nextprev = (integer_t) head;
		head->nextprev ^= (integer_t) n;
	}
	return n;
}

/* print each value in the list */
void print_values(const char *prefix, node_t *n)
{
	node_t *prev = NULL;
	while (n) {
		printf("%s: %d\n", prefix, n->value);
		node_t *tmp = n;
		n = (node_t *) (n->nextprev ^ (integer_t) prev);
		prev = tmp;
	}
}

int main(int argc, char *argv[])
{
	node_t *head = NULL;
	node_t *tail = NULL;

	/* create the first node, we always insert at the head so this node becomes the tail */
	head = tail = insert_at_head(head, new_node(4));

	/* insert a few more nodes */
	head = insert_at_head(head, new_node(3));
	head = insert_at_head(head, new_node(2));
	head = insert_at_head(head, new_node(1));

	/* iterate forward */
	print_values("forward", head);

	/* iterate_backward */
	print_values("backward", tail);

	return 0;
}