X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=src%2Fshared%2Fin-addr-util.c;h=9dc9ec82b484eb4c97976ab1de7d50cf9561eff0;hp=457eedd6d81825f519984f06884cc0c91ab4c6c0;hb=cfb1f5df7ce6868d3edb7333591b91c9809d64d3;hpb=44e7b9492617408130d11ffa451c2660942974f6

diff --git a/src/shared/in-addr-util.c b/src/shared/in-addr-util.c
index 457eedd6d..9dc9ec82b 100644
--- a/src/shared/in-addr-util.c
+++ b/src/shared/in-addr-util.c
@@ -248,3 +248,45 @@ unsigned in_addr_netmask_to_prefixlen(const struct in_addr *addr) {
 
         return 32 - u32ctz(be32toh(addr->s_addr));
 }
+
+int in_addr_default_prefixlen(const struct in_addr *addr, unsigned char *prefixlen) {
+        uint8_t msb_octet = *(uint8_t*) addr;
+
+        /* addr may not be aligned, so make sure we only access it byte-wise */
+
+        assert(addr);
+        assert(prefixlen);
+
+        if (msb_octet < 128)
+                /* class A, leading bits: 0 */
+                *prefixlen = 8;
+        else if (msb_octet < 192)
+                /* class B, leading bits 10 */
+                *prefixlen = 16;
+        else if (msb_octet < 224)
+                /* class C, leading bits 110 */
+                *prefixlen = 24;
+        else
+                /* class D or E, no default prefixlen */
+                return -ERANGE;
+
+        return 0;
+}
+
+int in_addr_default_subnet_mask(const struct in_addr *addr, struct in_addr *mask) {
+        unsigned char prefixlen;
+        int r;
+
+        assert(addr);
+        assert(mask);
+
+        r = in_addr_default_prefixlen(addr, &prefixlen);
+        if (r < 0)
+                return r;
+
+        assert(prefixlen > 0 && prefixlen < 32);
+
+        mask->s_addr = htobe32((0xffffffff << (32 - prefixlen)) & 0xffffffff);
+
+        return 0;
+}