timeformat.c

WWVB receiver using AVR.

/* $Id: timeformat.c,v 1.3 2006/01/19 20:52:23 simimeie Exp $
 * Routines for handling various time representations.
 * Mainly conversion routines from broken time to timestamps and the other
 * way round.
 */ 

#define BV _BV
#include <avr/io.h>
#include "timeformat.h"

/* The UNIX-Timestamp of 1.1.2000 */
static const uint32_t TS01012000 = 946681200UL;

/* On which day does a new month start in non-leap-years */
static const uint16_t monthstarts[12] = {   0,  31,  59,  90, 120, 151,
                                          181, 212, 243, 273, 304, 334 };

static const uint32_t SECONDSINADAY = (60UL * 60 * 24);

/* Converts a brokentime-struct to a timestamp */
uint32_t bttots(struct brokentime * bt) {
	uint32_t res = TS01012000 + SECONDSINADAY; /* 2000 was leap year */
	if ((bt->month == 0) || (bt->day == 0)) {
		/* Not a valid date */
		return 0;
	}
	res += SECONDSINADAY * bt->year * 365;
	/* Now account for the leap years. Yes, 2000 was a leap year too. */
	res += SECONDSINADAY * ((bt->year - 1) >> 2);
	res += SECONDSINADAY * monthstarts[bt->month - 1];
	if ((!(bt -> year & 3)) && (bt->month >= 3)) {
		/* We are in a leap year and past february */
		res += SECONDSINADAY;
	}
	res += SECONDSINADAY * (bt->day - 1);
	res += 3600UL * bt->hour;
	res += 60 * bt->min;
	res += bt->sec;
	return res;
}

/* Converts a timestamp to a brokentime-struct */
void tstobt(uint32_t ts, struct brokentime * bt) {
	uint8_t c = 0;
	if (ts < TS01012000) {
		bt->year = bt->month = bt->day = bt->hour = bt->min = bt->sec = 0;
		return;
	}
	ts -= TS01012000;
	while (1) {
		if (!(c & 3)) { /* Leap year */
			if (ts < (SECONDSINADAY * 366)) break;
			ts -= SECONDSINADAY * 366;
		} else {
			if (ts < (SECONDSINADAY * 365)) break;
			ts -= SECONDSINADAY * 365;
		}
		c++;
	}
	bt->year = c;
	for (c = 11; c; c--) {
		if ((SECONDSINADAY * monthstarts[c]) <= ts) break;
	}
	bt->month = c + 1;
	ts -= SECONDSINADAY * monthstarts[c];
	bt->day = (ts / SECONDSINADAY) + 1;
	ts = ts % SECONDSINADAY;
	if ((!(bt->year & 3)) && (bt->month >= 3)) { /* Leap year and >= 29.2. */
		bt->day--;
		if (bt->day == 0) {  /* Oups, we're at the end of the */
			bt->month--; /* previous month */
			switch (bt->month) {
			case  2: bt->day = 29; break;
			case  3: bt->day = 31; break;
			case  4: bt->day = 30; break;
			case  5: bt->day = 31; break;
			case  6: bt->day = 30; break;
			case  7: bt->day = 31; break;
			default: if (bt->day & 1) {
					bt->day = 30;
				 } else {
					bt->day = 31;
				 }
				 break;
			};
		}
	}
	bt->hour = (ts / 3600);
	ts = ts % 3600;
	bt->min = (ts / 60);
	bt->sec = (ts % 60);
}