}
int in_addr_default_prefixlen(const struct in_addr *addr, unsigned char *prefixlen) {
- uint32_t address;
+ uint8_t msb_octet = *(uint8_t*) addr;
+
+ /* addr may not be aligned, so make sure we only access it byte-wise */
assert(addr);
- assert(addr->s_addr != INADDR_ANY);
assert(prefixlen);
- address = be32toh(addr->s_addr);
-
- if ((address >> 31) == 0x0)
+ if (msb_octet < 128)
/* class A, leading bits: 0 */
*prefixlen = 8;
- else if ((address >> 30) == 0x2)
+ else if (msb_octet < 192)
/* class B, leading bits 10 */
*prefixlen = 16;
- else if ((address >> 29) == 0x6)
+ else if (msb_octet < 224)
/* class C, leading bits 110 */
*prefixlen = 24;
else