linuxptp/lstab.c

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/**
* @file lstab.c
* @note Copyright (C) 2012 Richard Cochran <richardcochran@gmail.com>
* @note SPDX-License-Identifier: GPL-2.0+
*/
#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
#include "lstab.h"
/*
* Keep a history of the TAI - UTC offset in a lookup table.
*
* Each entry gives the NTP time when a new TAI offset came into
* effect. This is always the second immediately after a leap second.
*
* The size of the table is the number of entries from the NIST table,
* plus room for two hundred more entries to be added at run time.
* Since there can be at most two leap seconds per year, this allows
* for at least one hundred years.
*
* The table data are available from
*
* https://www.ietf.org/timezones/data/leap-seconds.list
*
* ftp://ftp.nist.gov/pub/time/leap-seconds.list
*
* When updating this table, do not forget to set N_HISTORICAL_LEAPS
* and the expiration date.
*/
#define BASE_TAI_OFFSET 10
#define N_HISTORICAL_LEAPS 28
#define N_LEAPS (N_HISTORICAL_LEAPS + 200)
#define NTP_UTC_OFFSET 2208988800ULL
struct epoch_marker {
int offset; /* TAI - UTC offset of epoch */
uint64_t ntp; /* NTP time of epoch */
uint64_t tai; /* TAI time of epoch */
uint64_t utc; /* UTC time of epoch */
};
struct lstab {
struct epoch_marker lstab[N_LEAPS];
uint64_t expiration_utc;
int length;
};
static const uint64_t expiration_date_ntp = 3802291200ULL; /* 28 June 2020 */
static const uint64_t offset_table[N_LEAPS * 2] = {
2272060800ULL, 10, /* 1 Jan 1972 */
2287785600ULL, 11, /* 1 Jul 1972 */
2303683200ULL, 12, /* 1 Jan 1973 */
2335219200ULL, 13, /* 1 Jan 1974 */
2366755200ULL, 14, /* 1 Jan 1975 */
2398291200ULL, 15, /* 1 Jan 1976 */
2429913600ULL, 16, /* 1 Jan 1977 */
2461449600ULL, 17, /* 1 Jan 1978 */
2492985600ULL, 18, /* 1 Jan 1979 */
2524521600ULL, 19, /* 1 Jan 1980 */
2571782400ULL, 20, /* 1 Jul 1981 */
2603318400ULL, 21, /* 1 Jul 1982 */
2634854400ULL, 22, /* 1 Jul 1983 */
2698012800ULL, 23, /* 1 Jul 1985 */
2776982400ULL, 24, /* 1 Jan 1988 */
2840140800ULL, 25, /* 1 Jan 1990 */
2871676800ULL, 26, /* 1 Jan 1991 */
2918937600ULL, 27, /* 1 Jul 1992 */
2950473600ULL, 28, /* 1 Jul 1993 */
2982009600ULL, 29, /* 1 Jul 1994 */
3029443200ULL, 30, /* 1 Jan 1996 */
3076704000ULL, 31, /* 1 Jul 1997 */
3124137600ULL, 32, /* 1 Jan 1999 */
3345062400ULL, 33, /* 1 Jan 2006 */
3439756800ULL, 34, /* 1 Jan 2009 */
3550089600ULL, 35, /* 1 Jul 2012 */
3644697600ULL, 36, /* 1 Jul 2015 */
3692217600ULL, 37, /* 1 Jan 2017 */
};
static void epoch_marker_init(struct epoch_marker *ls, uint64_t val, int offset)
{
ls->ntp = val;
ls->utc = val - NTP_UTC_OFFSET;
ls->tai = val - NTP_UTC_OFFSET + offset;
ls->offset = offset;
}
static void lstab_init(struct lstab *lstab)
{
struct epoch_marker *ls;
uint64_t offset, val;
int i;
for (i = 0; i < N_HISTORICAL_LEAPS; i++) {
ls = lstab->lstab + i;
val = offset_table[2 * i];
offset = offset_table[2 * i + 1];
epoch_marker_init(ls, val, offset);
}
lstab->expiration_utc = expiration_date_ntp - NTP_UTC_OFFSET;
lstab->length = i;
}
void lstab_print(struct lstab *lstab, FILE *fp)
{
int i, len = lstab->length;
fprintf(fp, "%3s%12s%12s%12s%4s\n", "idx", "NTP", "TAI", "UTC", "OFF");
for (i = 0; i < len; i++) {
fprintf(fp, "%3d" "%12" PRIu64 "%12" PRIu64 "%12" PRIu64 "%4d\n", i,
lstab->lstab[i].ntp, lstab->lstab[i].tai,
lstab->lstab[i].utc, lstab->lstab[i].offset);
}
}
static int lstab_read(struct lstab *lstab, const char *name)
{
uint64_t expiration, val;
struct epoch_marker *ls;
int index = 0, offset;
char buf[1024];
FILE *fp;
fp = fopen(name, "r");
if (!fp) {
fprintf(stderr, "failed to open '%s' for reading: %m\n", name);
return -1;
}
while (1) {
if (!fgets(buf, sizeof(buf), fp)) {
break;
}
if (1 == sscanf(buf, "#@ %" PRIu64, &expiration)) {
lstab->expiration_utc = expiration - NTP_UTC_OFFSET;
continue;
}
if (2 == sscanf(buf, "%" PRIu64 " %d", &val, &offset)) {
ls = lstab->lstab + index;
epoch_marker_init(ls, val, offset);
index++;
}
}
if (!lstab->expiration_utc) {
fprintf(stderr, "missing expiration date in '%s'\n", name);
return -1;
}
lstab->length = index;
return 0;
}
struct lstab *lstab_create(const char *filename)
{
struct lstab *lstab = calloc(1, sizeof(*lstab));
if (!lstab) {
return NULL;
}
if (filename && filename[0]) {
if (lstab_read(lstab, filename)) {
free(lstab);
return NULL;
}
} else {
lstab_init(lstab);
}
return lstab;
}
void lstab_destroy(struct lstab *lstab)
{
free(lstab);
}
enum lstab_result lstab_utc2tai(struct lstab *lstab, uint64_t utctime,
int *tai_offset)
{
int epoch = -1, index, next;
if (utctime > lstab->expiration_utc) {
return LSTAB_UNKNOWN;
}
for (index = lstab->length - 1; index > -1; index--) {
if (utctime >= lstab->lstab[index].utc) {
epoch = index;
break;
}
}
if (epoch == -1) {
return LSTAB_UNKNOWN;
}
*tai_offset = lstab->lstab[epoch].offset;
next = epoch + 1;
if (next < lstab->length && utctime == lstab->lstab[next].utc - 1) {
return LSTAB_AMBIGUOUS;
}
return LSTAB_OK;
}