Исходное сообщение
"помогите пересчитать TCP checksum" Отправлено tcp, 27-Сен-06 13:13
>rfc-793 пункт 3.1 >что не понятно? как считаем? inline u_short in_cksum(u_short *addr, int len) {     register int nleft = len;     register u_short *w = addr;     register int sum = 0;     u_short answer = 0;      /* Our algorithm is simple, using a 32 bit accumulator (sum), we add       * sequential 16 bit words to it, and at the end, fold back all the       * carry bits from the top 16 bits into the lower 16 bits. */      while (nleft > 1)  {          sum += *w++;          nleft -= 2;      }      /* mop up an odd byte, if necessary */      if (nleft == 1) {          *(u_char *)(&answer) = *(u_char *) w;          sum += answer;      }      /* add back carry outs from top 16 bits to low 16 bits */      sum = (sum >> 16) + (sum & 0xffff); /* add hi 16 to low 16 */      sum += (sum >> 16);                /* add carry */      answer = ~sum;                     /* truncate to 16 bits */      return(answer); } struct cksum {     struct pseudo_hdr pseudo;     struct tcp_hdr tcp; }; tcp->th_sum           = in_cksum((void *)cksum, sizeof(struct cksum));