/*      $NetBSD: ntp_calgps.h,v 1.2 2020/05/25 20:47:19 christos Exp $  */

/*
* ntp_calgps.h - calendar for GPS/GNSS based clocks
*
* Written by Juergen Perlinger ([email protected]) for the NTP project.
* The contents of 'html/copyright.html' apply.
*
* --------------------------------------------------------------------
*
* This module implements stuff often used with GPS/GNSS receivers
*/
#ifndef NTP_CALGPS_H
#define NTP_CALGPS_H

#include <time.h>

#include "ntp_types.h"
#include "ntp_fp.h"
#include "ntp_calendar.h"

/* GPS week calendar (extended weeks)
* We use weeks based on 1899-31-12, which was the last Sunday before
* the begin of the NTP epoch. (Which is equivalent to saying 1900-01-01
* was a Monday...)
*
* We simply pre-calculate the offsets and cycle shifts for the real GPS
* calendar, which starts at 1980-01-06, to simplyfy some expressions.
*
* This has a fringe benefit that should not be overlooked: Since week zero
* is around 1900, and we should never have to deal with dates before
* 1970 or 1980, a week number of zero can be easily used to indicate
* an invalid week time stamp.
*/
#define GPSNTP_WSHIFT   4175    /* weeks 1899-31-12 --> 1980-01-06 */
#define GPSNTP_WCYCLE     79    /* above, modulo 1024 */
#define GPSNTP_DSHIFT      1    /* day number of 1900-01-01 in week */

struct gpsdatum {
       uint32_t weeks;         /* weeks since GPS epoch        */
       int32_t  wsecs;         /* seconds since week start     */
       uint32_t frac;          /* fractional seconds           */
};
typedef struct gpsdatum TGpsDatum;
typedef struct gpsdatum const TcGpsDatum;

/* NTP date/time in split representation */
struct ntpdatum {
       uint32_t days;          /* since NTP epoch              */
       int32_t  secs;          /* since midnight, denorm is ok */
       uint32_t frac;          /* fractional seconds           */
};
typedef struct ntpdatum TNtpDatum;
typedef struct ntpdatum const TcNtpDatum;

/*
* GPS week/sec calendar functions
*
* see the implementation for details, especially the
* 'gpscal_from_weektime{1,2}()'
*/

extern TGpsDatum
gpscal_fix_gps_era(TcGpsDatum *);

extern void
gpscal_add_offset(TGpsDatum *datum, l_fp offset);

extern TGpsDatum
gpscal_from_calendar_ex(TcCivilDate*, l_fp fofs, int/*BOOL*/ warp);

static inline TGpsDatum
gpscal_from_calendar(TcCivilDate *pCiv, l_fp fofs) {
   return gpscal_from_calendar_ex(pCiv, fofs, TRUE);
}

extern TGpsDatum        /* see source for semantic of the 'fofs' value! */
gpscal_from_gpsweek(uint16_t w, int32_t s, l_fp fofs);

extern TGpsDatum
gpscal_from_weektime1(int32_t wsecs, l_fp fofs, l_fp pivot);

extern TGpsDatum
gpscal_from_weektime2(int32_t wsecs, l_fp fofs, TcGpsDatum *pivot);

extern void
gpscal_to_calendar(TCivilDate*, TcGpsDatum*);

extern TGpsDatum
gpscal_from_gpsntp(TcNtpDatum*);

extern l_fp
ntpfp_from_gpsdatum(TcGpsDatum *);

/*
* NTP day/sec calendar functions
*
* see the implementation for details, especially the
* 'gpscal_from_daytime{1,2}()'
*/
extern TNtpDatum
gpsntp_fix_gps_era(TcNtpDatum *);

extern void
gpsntp_add_offset(TNtpDatum *datum, l_fp offset);

extern TNtpDatum
gpsntp_from_calendar_ex(TcCivilDate*, l_fp fofs, int/*BOOL*/ warp);

static inline TNtpDatum
gpsntp_from_calendar(TcCivilDate * pCiv, l_fp fofs) {
       return gpsntp_from_calendar_ex(pCiv, fofs, TRUE);
}

extern TNtpDatum
gpsntp_from_daytime1_ex(TcCivilDate *dt, l_fp fofs, l_fp pivot, int/*BOOL*/ warp);

static inline TNtpDatum
gpsntp_from_daytime1(TcCivilDate *dt, l_fp fofs, l_fp pivot) {
       return gpsntp_from_daytime1_ex(dt, fofs, pivot, TRUE);
}

extern TNtpDatum
gpsntp_from_daytime2_ex(TcCivilDate *dt, l_fp fofs, TcNtpDatum *pivot, int/*BOOL*/ warp);

static inline TNtpDatum
gpsntp_from_daytime2(TcCivilDate *dt, l_fp fofs, TcNtpDatum *pivot) {
       return gpsntp_from_daytime2_ex(dt, fofs, pivot, TRUE);
}

extern TNtpDatum
gpsntp_from_gpscal_ex(TcGpsDatum*, int/*BOOL*/ warp);

static inline TNtpDatum
gpsntp_from_gpscal(TcGpsDatum *wd) {
       return gpsntp_from_gpscal_ex(wd, FALSE);
}

extern void
gpsntp_to_calendar(TCivilDate*, TcNtpDatum*);

extern l_fp
ntpfp_from_ntpdatum(TcNtpDatum*);

/*
* Some helpers
*/

/* apply fudge to time stamp: *SUBTRACT* the given offset from an l_fp*/
extern l_fp
ntpfp_with_fudge(l_fp lfp, double ofs);

#endif /*!defined(NTP_CALGPS_H)*/