if (TST(icp->icmp_seq % mx_dup_ck)) {
			++nrepeats;
			--nreceived;
			dupflag = 1;
		} else {
			SET(icp->icmp_seq % mx_dup_ck);
			dupflag = 0;
		}

		if (options & F_QUIET)
			return;

		if (options & F_FLOOD)
			(void)write(STDOUT_FILENO, &BSPACE, 1);
		else {
			(void)printf("%d bytes from %s: icmp_seq=%u", cc,
			   inet_ntoa(*(struct in_addr *)&from->sin_addr.s_addr),
			   icp->icmp_seq);
			(void)printf(" ttl=%d", ip->ip_ttl);
			if (timing)
				(void)printf(" time=%ld.%ld ms", triptime/10,
						triptime%10);
			if (dupflag)
				(void)printf(" (DUP!)");
			/* check the data */
#ifndef icmp_data
			cp = ((u_char*)(icp + 1) + 8);
#else
			cp = (u_char*)icp->icmp_data + 8;
#endif
			dp = &outpack[8 + sizeof(struct timeval)];
			for (i = 8; i < datalen; ++i, ++cp, ++dp) {
				if (*cp != *dp) {
	(void)printf("\nwrong data byte #%d should be 0x%x but was 0x%x",
	    i, *dp, *cp);
					cp = (u_char*)(icp + 1);
					for (i = 8; i < datalen; ++i, ++cp) {
						if ((i % 32) == 8)
							(void)printf("\n\t");
						(void)printf("%x ", *cp);
					}
					break;
				}
			}
		}
	} else {
		/* We've got something other than an ECHOREPLY */
		if (!(options & F_VERBOSE))
			return;
		(void)printf("%d bytes from %s: ", cc,
		    pr_addr(from->sin_addr.s_addr));
		pr_icmph(icp);
	}

/*#if 0*/
	/*顯示其他IP選項 */
	cp = (u_char *)buf + sizeof(struct iphdr);

	for (; hlen > (int)sizeof(struct iphdr); --hlen, ++cp)
		switch (*cp) {
		case IPOPT_EOL:
			hlen = 0;
			break;
		case IPOPT_LSRR:
			(void)printf("\nLSRR: ");
			hlen -= 2;
			j = *++cp;
			++cp;
			if (j > IPOPT_MINOFF)
				for (;;) {
					l = *++cp;
					l = (l<<8) + *++cp;
					l = (l<<8) + *++cp;
					l = (l<<8) + *++cp;
					if (l == 0)
						(void)printf("\t0.0.0.0");
				else
					(void)printf("\t%s", pr_addr(ntohl(l)));
				hlen -= 4;
				j -= 4;
				if (j <= IPOPT_MINOFF)
					break;
				(void)putchar('\n');
			}
			break;
		case IPOPT_RR:
			j = *++cp;		/* get length */
			i = *++cp;		/* and pointer */
			hlen -= 2;
			if (i > j)
				i = j;
			i -= IPOPT_MINOFF;
			if (i <= 0)
				continue;
			if (i == old_rrlen
			    && cp == (u_char *)buf + sizeof(struct iphdr) + 2
			    && !memcmp((char *)cp, old_rr, i)
			    && !(options & F_FLOOD)) {
				(void)printf("\t(same route)");
				i = ((i + 3) / 4) * 4;
				hlen -= i;
				cp += i;
				break;
			}
			old_rrlen = i;
			memcpy(old_rr, cp, i);
			(void)printf("\nRR: ");
			for (;;) {
				l = *++cp;
				l = (l<<8) + *++cp;
				l = (l<<8) + *++cp;
				l = (l<<8) + *++cp;
				if (l == 0)
					(void)printf("\t0.0.0.0");
				else
					(void)printf("\t%s", pr_addr(ntohl(l)));
				hlen -= 4;
				i -= 4;
				if (i <= 0)
					break;
				(void)putchar('\n');
			}
			break;
		case IPOPT_NOP:
			(void)printf("\nNOP");
			break;
		default:
			(void)printf("\nunknown option %x", *cp);
			break;
		}
/*#endif*/
	if (!(options & F_FLOOD)) {
		(void)putchar('\n');
		(void)fflush(stdout);
	}
}
in_cksum是數據校驗程序，如下所示：
static int
in_cksum(u_short *addr, int len)
{
	register int nleft = len;
	register u_short *w = addr;
	register int sum = 0;
	u_short answer = 0;

	/*這里的算法很簡單，就采用32bit的加法*/
	while (nleft > 1)  {
		sum += *w++;
		nleft -= 2;
	}

	if (nleft == 1) {
		*(u_char *)(&answer) = *(u_char *)w ;
		sum += answer;
	}

	/*把高16bit加到低16bit上去*/
	sum = (sum >> 16) + (sum & 0xffff);
	sum += (sum >> 16);
	answer = ~sum;
	return(answer);
}
Finish程序是ping程序的結束程序，主要是打印出來一些統計信息，如下所示：
static void
finish(int ignore)
{
	(void)ignore;

	(void)signal(SIGINT, SIG_IGN);
	(void)putchar('\n');
	(void)fflush(stdout);
	(void)printf("--- %s ping statistics ---\n", hostname);
	(void)printf("%ld packets transmitted, ", ntransmitted);
	(void)printf("%ld packets received, ", nreceived);
	if (nrepeats)
		(void)printf("+%ld duplicates, ", nrepeats);
	if (ntransmitted)
		if (nreceived > ntransmitted)
			(void)printf("-- somebody's printing up packets!");
		else
			(void)printf("%d%% packet loss",
			    (int) (((ntransmitted - nreceived) * 100) /
			    ntransmitted));
	(void)putchar('\n');
	if (nreceived && timing)
		(void)printf("round-trip min/avg/max = %ld.%ld/%lu.%ld/%ld.%ld ms\n",
			tmin/10, tmin%10,
			(tsum / (nreceived + nrepeats))/10,
			(tsum / (nreceived + nrepeats))%10,
			tmax/10, tmax%10);

	if (nreceived==0) exit(1);
	exit(0);
}

#ifdef notdef
static char *ttab[] = {
	"Echo Reply",		/* ip + seq + udata */
	"Dest Unreachable",	/* net, host, proto, port, frag, sr + IP */
	"Source Quench",	/* IP */
	"Redirect",		/* redirect 類型, gateway, + IP  */
	"Echo",
	"Time Exceeded",	/*傳輸超時*/
	"Parameter Problem",	/* IP參數問題 */
	"Timestamp",		/* id + seq + three timestamps */
	"Timestamp Reply",	/* " */
	"Info Request",		/* id + sq */
	"Info Reply"		/* " */
};
#endif
pr_icmph函數是用于打印出ICMP回應信息，如下所示：
static void
pr_icmph(struct icmphdr *icp)
{
	switch(icp->icmp_type) {
/*ICMP回應*/
	case ICMP_ECHOREPLY:
		(void)printf("Echo Reply\n");
		/* XXX ID + Seq + Data */
		break;
/*ICMP終點不可達*/
	case ICMP_DEST_UNREACH:
		switch(icp->icmp_code) {
		case ICMP_NET_UNREACH:
			(void)printf("Destination Net Unreachable\n");
			break;
		case ICMP_HOST_UNREACH:
			(void)printf("Destination Host Unreachable\n");
			break;
		case ICMP_PROT_UNREACH:
			(void)printf("Destination Protocol Unreachable\n");
			break;
		…
		default:
			(void)printf("Dest Unreachable, Unknown Code: %d\n",
			    icp->icmp_code);
			break;
		}
		/* Print returned IP header information */
#ifndef icmp_data
		pr_retip((struct iphdr *)(icp + 1));
#else
		pr_retip((struct iphdr *)icp->icmp_data);
#endif
		break;
		…
		default:
			(void)printf("Redirect, Bad Code: %d", icp->icmp_code);
			break;
		}
		(void)printf("(New addr: %s)\n", 
			     inet_ntoa(icp->icmp_gwaddr));
#ifndef icmp_data
		pr_retip((struct iphdr *)(icp + 1));
#else
		pr_retip((struct iphdr *)icp->icmp_data);
#endif
		break;
	case ICMP_ECHO:
		(void)printf("Echo Request\n");
		/* XXX ID + Seq + Data */
		break;
	case ICMP_TIME_EXCEEDED:
		switch(icp->icmp_code) {
		case ICMP_EXC_TTL:
			(void)printf("Time to live exceeded\n");
			break;
		case ICMP_EXC_FRAGTIME:
			(void)printf("Frag reassembly time exceeded\n");
			break;
		default:
			(void)printf("Time exceeded, Bad Code: %d\n",
			    icp->icmp_code);
			break;
		}
	…
	default:
		(void)printf("Bad ICMP type: %d\n", icp->icmp_type);
	}
}
pr_iph函數是用于打印IP數據包頭選項，如下所示：
static void
pr_iph(struct iphdr *ip)
{
	int hlen;
	u_char *cp;

	hlen = ip->ip_hl << 2;
	cp = (u_char *)ip + 20;		/* point to options */
	(void)printf("Vr HL TOS  Len   ID Flg  off TTL Pro  cks      Src      Dst Data\n");
	(void)printf(" %1x  %1x  %02x %04x %04x",
	    ip->ip_v, ip->ip_hl, ip->ip_tos, ip->ip_len, ip->ip_id);
	(void)printf("   %1x %04x", ((ip->ip_off) & 0xe000) >> 13,
	    (ip->ip_off) & 0x1fff);
	(void)printf("  %02x  %02x %04x", ip->ip_ttl, ip->ip_p, ip->ip_sum);
	(void)printf(" %s ", inet_ntoa(*((struct in_addr *) &ip->ip_src)));
	(void)printf(" %s ", inet_ntoa(*((struct in_addr *) &ip->ip_dst)));
	/* dump and option bytes */
	while (hlen-- > 20) {
		(void)printf("%02x", *cp++);
	}
	(void)putchar('\n');
}
pr_addr是用于將ascii主機地址轉換為十進制點分形式并打印出來，這里使用的函數是inet_ntoa，如下所示：
static char *
pr_addr(u_long l)
{
	struct hostent *hp;
	static char buf[256];

	if ((options & F_NUMERIC) ||
	    !(hp = gethostbyaddr((char *)&l, 4, AF_INET)))
		(void)sprintf(buf, /*sizeof(buf),*/ "%s",inet_ntoa(*(struct in_addr *)&l));
	else
		(void)sprintf(buf, /*sizeof(buf),*/ "%s (%s)", hp->h_name,inet_ntoa(*(struct in_addr *)&l));
	return(buf);
}
Usage函數是用于顯示幫助信息，如下所示：
static void
usage(void)
{
	(void)fprintf(stderr,
	    "usage: ping [-LRdfnqrv] [-c count] [-i wait] [-l preload]\n\t[-p pattern] [-s packetsize] [-t ttl] [-I interface address] host\n");
	exit(2);
}