/***************************************************************************
* __________ __ ___.
* Open \______ \ ____ ____ | | _\_ |__ _______ ___
* Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ /
* Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < <
* Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \
* \/ \/ \/ \/ \/
* $Id$
*
* Copyright (C) 2017 by Michael Sevakis
*
* Copyright (C) 2012 by Bertrik Sikken
*
* Based on code from: rtc_as3514.c
* Copyright (C) 2007 by Barry Wardell
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
* KIND, either express or implied.
*
****************************************************************************/
#include "time.h"
/* Constants that mark Thursday, 1 January 1970 */
#define UNIX_EPOCH_DAY_NUM 134774
#define UNIX_EPOCH_YEAR (1601 - 1900)
/* Last day number it can do */
#define MAX_DAY_NUM 551879
/* d is days since epoch start, Monday, 1 January 1601 (d = 0)
*
* That date is the beginning of a full 400 year cycle and so simplifies the
* calculations a bit, not requiring offsets before divisions to shift the
* leap year cycle.
*
* It can handle dates up through Sunday, 31 December 3111 (d = 551879).
*
* time_t can't get near the limits anyway for now but algorithm can be
* altered slightly to increase range if even needed.
*/
static void get_tmdate(unsigned int d, struct tm *tm)
{
static const unsigned short mon_yday[13] =
{
/* year day of 1st of month (non-leap)
+31 +28 +31 +30 +31 +30 +31 +31 +30 +31 +30 +31 +31 */
0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365
};
unsigned int x0, x1, x2, x3; /* scratch variables */
/* calculate year from day number */
x0 = d / 1460;
x1 = x0 / 25;
x2 = x1 / 4;
unsigned int y = (d - x0 + x1 - x2) / 365;
tm->tm_year = y + UNIX_EPOCH_YEAR; /* year - 1900 */
/* calculate year day from year number and day number */
x0 = y / 4;
x1 = x0 / 25;
x2 = x1 / 4;
unsigned int yday = d - x0 + x1 - x2 - y * 365;
tm->tm_yday = x3 = yday; /* 0..364/365 */
/* check if leap year; adjust February->March transition if so rather
than keeping a leap year version of mon_yday[] */
if (y - x0 * 4 == 3 && (x0 - x1 * 25 != 24 || x1 - x2 * 4 == 3)) {
/* retard month lookup to make year day 59 into 29 Feb, both to make
year day 60 into 01 March, lagging one day for remainder of year */
if (x3 >= mon_yday[2] && --x3 >= mon_yday[2]) {
yday--;
}
}
/* stab approximately at current month based on year day; advance if
it fell short (never initially more than 1 short). */
x0 = x3 / 32;
if (mon_yday[x0 + 1] <= x3) {
x0++;
}
tm->tm_mon = x0; /* 0..11 */
tm->tm_mday = yday - mon_yday[x0] + 1; /* 1..31 */
tm->tm_wday = (d + 1) % 7; /* 0..6 */
}
struct tm * gmtime_r(const time_t *timep, struct tm *tm)
{
time_t t = *timep;
int d = t / 86400; /* day number (-24856..24855) */
int s = t - (time_t)d * 86400; /* second # of day (0..86399) */
if (s < 0) {
/* round towards 0 -> floored division */
d--;
s += 86400;
}
unsigned int x;
x = s / 3600;
tm->tm_hour = x; /* 0..23 */
s -= x * 3600;
x = s / 60;
tm->tm_min = x; /* 0..59 */
s -= x * 60;
tm->tm_sec = s; /* 0..59 */
/* not implemented right now */
tm->tm_isdst = -1;
get_tmdate(d + UNIX_EPOCH_DAY_NUM, tm);
return tm;
}
struct tm * gmtime(const time_t *timep)
{
static struct tm time;
return gmtime_r(timep, &time);
}