--- a/src/common/vclock.c	Wed Jul 01 20:18:39 2015 -0400
+++ b/src/common/vclock.c	Wed Jul 01 20:22:14 2015 -0400
@@ -186,10 +186,114 @@
 	return nvclock_inc_node(clock, nomad_local_node_id());
 }
 
+static int vc_cmp(const void *va, const void *vb)
+{
+	const struct nvclockent *a = va;
+	const struct nvclockent *b = vb;
+
+	if (a->node < b->node)
+		return -1;
+	if (a->node > b->node)
+		return 1;
+	return 0;
+}
+
+/*
+ * Are all elements in @u <= than their corresponding elements in @v?
+ */
+static bool all_le(struct nvclock *u, int i, struct nvclock *v, int j)
+{
+	while ((i < NVCLOCK_NUM_NODES) && (j < NVCLOCK_NUM_NODES)) {
+		struct nvclockent *a = &u->ent[i];
+		struct nvclockent *b = &v->ent[j];
+
+
+		if (a->node < b->node) {
+			/*
+			 * @v doesn't have this node, therefore it is
+			 * assumed to be zero.  Since @u's element won't be
+			 * zero (otherwise it'd be omitted), we are
+			 * essentially asking this question:
+			 *
+			 * x <= 0, where x >= 1
+			 *
+			 * which is obviously false.
+			 */
+			return false;
+		}
+
+		if (a->node == b->node) {
+			if (a->seq > b->seq)
+				return false;
+
+			/* advance both */
+			i++;
+			j++;
+		} else {
+			/* let @u catch up */
+			i++;
+		}
+	}
+
+	return true;
+}
+
 enum nvclockcmp nvclock_cmp(const struct nvclock *c1, const struct nvclock *c2)
 {
-#warning "not yet implemented"
-	// XXX: actually compare
+	struct nvclock u, v;
+	int i, j;
+
+	u = *c1;
+	v = *c2;
+
+	qsort(u.ent, NVCLOCK_NUM_NODES, sizeof(struct nvclockent), vc_cmp);
+	qsort(v.ent, NVCLOCK_NUM_NODES, sizeof(struct nvclockent), vc_cmp);
+
+	/* find first non-zero node */
+	for (i = 0; i < NVCLOCK_NUM_NODES; i++)
+		if (u.ent[i].node)
+			break;
+
+	for (j = 0; j < NVCLOCK_NUM_NODES; j++)
+		if (v.ent[j].node)
+			break;
+
+	/* handle some trivial cases (one or both vectors being empty */
+	if (i == NVCLOCK_NUM_NODES && j == NVCLOCK_NUM_NODES)
+		return NVC_EQ;
+	if (i == NVCLOCK_NUM_NODES)
+		return NVC_LT;
+	if (j == NVCLOCK_NUM_NODES)
+		return NVC_GT;
+
+	/*
+	 * We have two non-empty vectors.
+	 */
+	if (i == j) {
+		bool all_eq;
+		int tmp;
+
+		/*
+		 * Both vectors have the same number of elements so they
+		 * have a chance of being equal
+		 */
+		all_eq = true;
+
+		for (tmp = i; all_eq && (tmp < NVCLOCK_NUM_NODES); tmp++)
+			all_eq = ((u.ent[tmp].node == v.ent[tmp].node) &&
+				  (u.ent[tmp].seq == v.ent[tmp].seq));
+
+		if (all_eq)
+			return NVC_EQ;
+	}
+
+	if (all_le(&u, i, &v, j))
+		return NVC_LT;
+
+	if (all_le(&v, j, &u, i))
+		return NVC_GT;
+
+	return NVC_DIV;
 }
 
 int nvclock_cmp_total(const struct nvclock *c1, const struct nvclock *c2)