Added ipa_class_mask() which guesses netmask for classful addressing.

For pure A/B/C class addresses it just returns the class netmask, for
subnets it tries to guess subnet mask. Please make sure the address
you pass to this function is really a valid host address (i.e., call
ipa_validate() first).

1 files changed, 16 insertions, 1 deletions

diff --git a/lib/ipv4.c b/lib/ipv4.c
index 9aa79c2..5ec2ffb 100644
--- a/lib/ipv4.c
+++ b/lib/ipv4.c
@@ -43,11 +43,26 @@ ip_ntop(ip_addr a, char *b)
 		      (x & 0xff));
 }
 
-
 char *
 ip_ntox(ip_addr a, char *b)
 {
   return b + bsprintf(b, "%08x", _I(a));
 }
 
+u32
+ipv4_class_mask(u32 a)
+{
+	u32 m;
+
+	if (a < 0x80000000)
+		m = 0xff000000;
+	if (a < 0xc0000000)
+		m = 0xffff0000;
+	else
+		m = 0xffffff00;
+	while (a & ~m)
+		m |= m >> 1;
+	return m;
+}
+
 #endif