shared: add nm_ppdirect_hash()/nm_ppdirect_equal() helpers

Useful for hashing pointers to a pointer to a pointer, and
compare the resulting pointer directly. This will be actually
used.

shared/nm-glib-aux/nm-hash-utils.c

@@ -206,3 +206,34 @@ nm_pdirect_equal (gconstpointer a, gconstpointer b)
 	           && s2
 	           && *s1 == *s2);
 }
+
+guint
+nm_ppdirect_hash (gconstpointer p)
+{
+	const void *const*const*s = p;
+
+	if (!s)
+		return nm_hash_static (396534869u);
+	if (!*s)
+		return nm_hash_static (1476102263u);
+	return nm_direct_hash (**s);
+}
+
+gboolean
+nm_ppdirect_equal (gconstpointer a, gconstpointer b)
+{
+	const void *const*const*s1 = a;
+	const void *const*const*s2 = b;
+
+	if (s1 == s2)
+		return TRUE;
+	if (!s1 || !s2)
+		return FALSE;
+
+	if (*s1 == *s2)
+		return TRUE;
+	if (!*s1 || !*s2)
+		return FALSE;
+
+	return **s1 == **s2;
+}

shared/nm-glib-aux/nm-hash-utils.h

@@ -279,12 +279,20 @@ gboolean nm_pstr_equal (gconstpointer a, gconstpointer b);
 /*****************************************************************************/
 
 /* this hashes/compares the pointer value that we point to. Basically,
- * (((const void *const*) a) == ((const void *const*) b)). */
+ * (*((const void *const*) a) == *((const void *const*) b)). */
 
 guint nm_pdirect_hash (gconstpointer p);
 
 gboolean nm_pdirect_equal (gconstpointer a, gconstpointer b);
 
+/* this hashes/compares the direct pointer value by following pointers to
+ * pointers 2 times.
+ * (**((const void *const*const*) a) == **((const void *const*const*) b)). */
+
+guint nm_ppdirect_hash (gconstpointer p);
+
+gboolean nm_ppdirect_equal (gconstpointer a, gconstpointer b);
+
 /*****************************************************************************/
 
 #define NM_HASH_OBFUSCATE_PTR_FMT "%016" G_GINT64_MODIFIER "x"