diff options
Diffstat (limited to 'firmware')
| -rw-r--r-- | firmware/libc/gmtime.c | 154 |
1 files changed, 86 insertions, 68 deletions
diff --git a/firmware/libc/gmtime.c b/firmware/libc/gmtime.c index c5deb59..b010509 100644 --- a/firmware/libc/gmtime.c +++ b/firmware/libc/gmtime.c @@ -7,6 +7,8 @@ * \/ \/ \/ \/ \/ * $Id$ * + * Copyright (C) 2017 by Michael Sevakis + * * Copyright (C) 2012 by Bertrik Sikken * * Based on code from: rtc_as3514.c @@ -21,96 +23,112 @@ * KIND, either express or implied. * ****************************************************************************/ -#include <stdbool.h> -#include <stdint.h> #include "time.h" -#define MINUTE_SECONDS 60 -#define HOUR_SECONDS 3600 -#define DAY_SECONDS 86400 -#define WEEK_SECONDS 604800 -#define YEAR_SECONDS 31536000 -#define LEAP_YEAR_SECONDS 31622400 +/* Constants that mark Thursday, 1 January 1970 */ +#define UNIX_EPOCH_DAY_NUM 134774 +#define UNIX_EPOCH_YEAR (1601 - 1900) -/* Days in each month */ -static uint8_t days_in_month[] = - {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}; +/* Last day number it can do */ +#define MAX_DAY_NUM 551879 -static inline bool is_leapyear(int year) +/* 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) { - return (((year%4)==0) && (((year%100)!=0) || ((year%400)==0))); -} + 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 + }; -struct tm *gmtime(const time_t *timep) -{ - static struct tm time; - return gmtime_r(timep, &time); -} + unsigned int x0, x1, x2, x3; /* scratch variables */ -struct tm *gmtime_r(const time_t *timep, struct tm *tm) -{ - time_t seconds = *timep; - int year, i, mday, hour, min; + /* calculate year from day number */ + x0 = d / 1460; + x1 = x0 / 25; + x2 = x1 / 4; - /* weekday */ - tm->tm_wday = (seconds / DAY_SECONDS + 4) % 7; + unsigned int y = (d - x0 + x1 - x2) / 365; - /* Year */ - year = 1970; - while (seconds >= LEAP_YEAR_SECONDS) - { - if (is_leapyear(year)){ - seconds -= LEAP_YEAR_SECONDS; - } else { - seconds -= YEAR_SECONDS; - } + tm->tm_year = y + UNIX_EPOCH_YEAR; /* year - 1900 */ - year++; - } + /* 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; - if (is_leapyear(year)) { - days_in_month[1] = 29; - } else { - days_in_month[1] = 28; - if(seconds>YEAR_SECONDS){ - year++; - seconds -= YEAR_SECONDS; + 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--; } } - tm->tm_year = year - 1900; - /* Month */ - for (i = 0; i < 12; i++) - { - if (seconds < days_in_month[i]*DAY_SECONDS){ - tm->tm_mon = i; - break; - } + /* 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) */ - seconds -= days_in_month[i]*DAY_SECONDS; + if (s < 0) { + /* round towards 0 -> floored division */ + d--; + s += 86400; } - /* Month Day */ - mday = seconds/DAY_SECONDS; - seconds -= mday*DAY_SECONDS; - tm->tm_mday = mday + 1; /* 1 ... 31 */ + unsigned int x; - /* Hour */ - hour = seconds/HOUR_SECONDS; - seconds -= hour*HOUR_SECONDS; - tm->tm_hour = hour; + x = s / 3600; + tm->tm_hour = x; /* 0..23 */ - /* Minute */ - min = seconds/MINUTE_SECONDS; - seconds -= min*MINUTE_SECONDS; - tm->tm_min = min; + s -= x * 3600; + x = s / 60; + tm->tm_min = x; /* 0..59 */ - /* Second */ - tm->tm_sec = seconds; + s -= x * 60; + tm->tm_sec = s; /* 0..59 */ - tm->tm_yday = 0; /* Not implemented for now */ - tm->tm_isdst = -1; /* Not implemented for now */ + /* 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); +} |