network: Implement bit length function for IPv4

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>

src/libloc/private.h

@@ -94,7 +94,7 @@ static inline struct in6_addr loc_prefix_to_bitmask(const unsigned int prefix) {
 	return bitmask;
 }
 
-static inline unsigned int loc_address_bit_length(const struct in6_addr* address) {
+static inline unsigned int __loc_address6_bit_length(const struct in6_addr* address) {
 	unsigned int length = 128;
 
 	for (int octet = 0; octet <= 15; octet++) {
@@ -108,6 +108,27 @@ static inline unsigned int loc_address_bit_length(const struct in6_addr* address
 	return length;
 }
 
+static inline unsigned int __loc_address4_bit_length(const struct in6_addr* address) {
+	unsigned int length = 32;
+
+	for (int octet = 12; octet <= 15; octet++) {
+		if (address->s6_addr[octet]) {
+			length -= __builtin_clz(address->s6_addr[octet]) - 24;
+			break;
+		} else
+			length -= 8;
+	}
+
+	return length;
+}
+
+static inline unsigned int loc_address_bit_length(const struct in6_addr* address) {
+	if (IN6_IS_ADDR_V4MAPPED(address))
+		return __loc_address4_bit_length(address);
+	else
+		return __loc_address6_bit_length(address);
+}
+
 static inline struct in6_addr loc_address_and(
 		const struct in6_addr* address, const struct in6_addr* bitmask) {
 	struct in6_addr a;

src/test-network.c

@@ -311,6 +311,8 @@ int main(int argc, char** argv) {
 	} bit_length_tests[] = {
 		{ "::/0", 0 },
 		{ "2001::/128", 126 },
+		{ "1.0.0.0/32", 25 },
+		{ "255.255.255.255/32", 32 },
 		{ NULL, 0, },
 	};