--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libnumutil/nanp_valid.c	Tue Dec 12 23:52:50 2023 +0000
@@ -0,0 +1,23 @@
+/*
+ * Utility functions for NANP number validation.
+ */
+
+#include <stdbool.h>
+
+#include <themwi/nanp/number_utils.h>
+
+bool is_nanp_valid_prefix(const char *s)
+{
+	/* validate NPA part */
+	if (s[0] < '2')
+		return false;
+	if (s[1] == '1' && s[2] == '1')
+		return false;
+	/* validate exchange part */
+	if (s[3] < '2')
+		return false;
+	if (s[4] == '1' && s[5] == '1')
+		return false;
+	/* all checks passed */
+	return true;
+}