sntp_proc.c

ntp协议实现针对服务器校时 c 源码

#include	"sntp.h"

void
sntp_proc(char *buf, ssize_t n, struct timeval *nowptr)
{
	int				version, mode;
	uint32_t		nsec, useci;
	double			usecf;
	struct timeval	curr, diff;
	struct ntpdata	*ntp;

	if (n < sizeof(struct ntpdata)) {
		printf("\npacket too small: %d bytes\n", n);
		return;
	}

	ntp = (struct ntpdata *) buf;
	version = (ntp->status & VERSION_MASK) >> 3;
	mode = ntp->status & MODE_MASK;
	printf("\nv%d, mode %d, strat %d, ", version, mode, ntp->stratum);
	if (mode == MODE_CLIENT) {
		printf("client\n");
		return;
	}

	nsec = ntohl(ntp->xmt.int_part) - JAN_1970;
	useci = htonl(ntp->xmt.fraction);	/* 32-bit integer fraction */
	usecf = useci;				/* integer fraction -> double */
	usecf /= 4294967296.0;		/* divide by 2**32 -> [0, 1.0) */
	useci = usecf * 1000000.0;	/* fraction -> parts per million */

	curr = *nowptr;		/* make a copy as we might modify it below */
	if ( (diff.tv_usec = curr.tv_usec - useci) < 0) {
		diff.tv_usec += 1000000;
		curr.tv_sec--;
	}
	diff.tv_sec = curr.tv_sec - nsec;
	useci = (diff.tv_sec * 1000000) + diff.tv_usec;	/* diff in microsec */
	printf("clock difference = %d usec\n", useci);
}