memcpy(&addr, arp.arp_tpa, sizeof addr); /* save protocol addr */
memcpy(arp.arp_tpa, arp.arp_spa, sizeof addr); /* swap destination and source protocol address */
memcpy(arp.arp_spa, &addr, sizeof addr); /* ... */
memcpy(&addr, arp.arp_tpa, sizeof addr); /* save protocol addr */
memcpy(arp.arp_tpa, arp.arp_spa, sizeof addr); /* swap destination and source protocol address */
memcpy(arp.arp_spa, &addr, sizeof addr); /* ... */