/* include sig_alrm */#include	"udpcksum.h"#include	<setjmp.h>static sigjmp_buf	jmpbuf;static int			canjump;voidsig_alrm(int signo){	if (canjump == 0)		return;	siglongjmp(jmpbuf, 1);}/* end sig_alrm *//* include test_udp */voidtest_udp(void){	volatile int	nsent = 0, timeout = 3;	struct udpiphdr	*ui;	Signal(SIGALRM, sig_alrm);	if (sigsetjmp(jmpbuf, 1)) {		if (nsent >= 3)			err_quit("no response");		printf("timeout\n");		timeout *= 2;		/* exponential backoff: 3, 6, 12 */	}	canjump = 1;	/* siglongjmp is now OK */	send_dns_query();	nsent++;	alarm(timeout);	ui = udp_read();	canjump = 0;	alarm(0);	if (ui->ui_sum == 0)		printf("UDP checksums off\n");	else		printf("UDP checksums on\n");	if (verbose)		printf("received UDP checksum = %x\n", ntohs(ui->ui_sum));}/* end test_udp */