[z180-stamp.git] / time / gmtime_r.c

/*
 * (C)2012 Michael Duane Rice All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 * Redistributions of source code must retain the above copyright notice, this
 * list of conditions and the following disclaimer. Redistributions in binary
 * form must reproduce the above copyright notice, this list of conditions
 * and the following disclaimer in the documentation and/or other materials
 * provided with the distribution. Neither the name of the copyright holders
 * nor the names of contributors may be used to endorse or promote products
 * derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/* $Id: gmtime_r.c 2369 2013-04-28 14:19:35Z swfltek $ */

/* Re entrant version of gmtime(). */

#include <time.h>
#include <stdlib.h>
#include <inttypes.h>

void
gmtime_r(const time_t * timer, struct tm * timeptr)
{
    int32_t         fract;
    ldiv_t          lresult;
    div_t           result;
    uint16_t        days, n, leapyear, years;

    /* break down timer into whole and fractional parts of 1 day */
    days = *timer / 86400UL;
    fract = *timer % 86400UL;

    /*
            Extract hour, minute, and second from the fractional day
        */
    lresult = ldiv(fract, 60L);
    timeptr->tm_sec = lresult.rem;
    result = div(lresult.quot, 60);
    timeptr->tm_min = result.rem;
    timeptr->tm_hour = result.quot;

    /* Determine day of week ( the epoch was a Saturday ) */
    n = days + SATURDAY;
    n %= 7;
    timeptr->tm_wday = n;

    /*
        * Our epoch year has the property of being at the conjunction of all three 'leap cycles',
        * 4, 100, and 400 years ( though we can ignore the 400 year cycle in this library).
        *
        * Using this property, we can easily 'map' the time stamp into the leap cycles, quickly
        * deriving the year and day of year, along with the fact of whether it is a leap year.
        */

    /* map into a 100 year cycle */
    lresult = ldiv((long) days, 36525L);
    years = 100 * lresult.quot;

    /* map into a 4 year cycle */
    lresult = ldiv(lresult.rem, 1461L);
    years += 4 * lresult.quot;
    days = lresult.rem;
    if (years > 100)
        days++;

    /*
         * 'years' is now at the first year of a 4 year leap cycle, which will always be a leap year,
         * unless it is 100. 'days' is now an index into that cycle.
         */
    leapyear = 1;
    if (years == 100)
        leapyear = 0;

    /* compute length, in days, of first year of this cycle */
    n = 364 + leapyear;

    /*
     * if the number of days remaining is greater than the length of the
     * first year, we make one more division.
     */
    if (days > n) {
        days -= leapyear;
        leapyear = 0;
        result = div(days, 365);
        years += result.quot;
        days = result.rem;
    }
    timeptr->tm_year = 100 + years;
    timeptr->tm_yday = days;

    /*
            Given the year, day of year, and leap year indicator, we can break down the
            month and day of month. If the day of year is less than 59 (or 60 if a leap year), then
            we handle the Jan/Feb month pair as an exception.
        */
    n = 59 + leapyear;
    if (days < n) {
        /* special case: Jan/Feb month pair */
        result = div(days, 31);
        timeptr->tm_mon = result.quot;
        timeptr->tm_mday = result.rem;
    } else {
        /*
            The remaining 10 months form a regular pattern of 31 day months alternating with 30 day
            months, with a 'phase change' between July and August (153 days after March 1).
            We proceed by mapping our position into either March-July or August-December.
            */
        days -= n;
        result = div(days, 153);
        timeptr->tm_mon = 2 + result.quot * 5;

        /* map into a 61 day pair of months */
        result = div(result.rem, 61);
        timeptr->tm_mon += result.quot * 2;

        /* map into a month */
        result = div(result.rem, 31);
        timeptr->tm_mon += result.quot;
        timeptr->tm_mday = result.rem;
    }

    /*
            Cleanup and return
        */
    timeptr->tm_isdst = 0;  /* gmt is never in DST */
    timeptr->tm_mday++; /* tm_mday is 1 based */

}
Commit	Line	Data
e63b2f75 L	1	/*
	2	* (C)2012 Michael Duane Rice All rights reserved.
	3	*
	4	* Redistribution and use in source and binary forms, with or without
	5	* modification, are permitted provided that the following conditions are
	6	* met:
	7	*
	8	* Redistributions of source code must retain the above copyright notice, this
	9	* list of conditions and the following disclaimer. Redistributions in binary
	10	* form must reproduce the above copyright notice, this list of conditions
	11	* and the following disclaimer in the documentation and/or other materials
	12	* provided with the distribution. Neither the name of the copyright holders
	13	* nor the names of contributors may be used to endorse or promote products
	14	* derived from this software without specific prior written permission.
	15	*
	16	* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
	17	* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	18	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	19	* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
	20	* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
	21	* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
	22	* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
	23	* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
	24	* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
	25	* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
	26	* POSSIBILITY OF SUCH DAMAGE.
	27	*/
	28
	29	/* $Id: gmtime_r.c 2369 2013-04-28 14:19:35Z swfltek $ */
	30
	31	/* Re entrant version of gmtime(). */
	32
	33	#include <time.h>
	34	#include <stdlib.h>
	35	#include <inttypes.h>
	36
	37	void
	38	gmtime_r(const time_t * timer, struct tm * timeptr)
	39	{
	40	int32_t fract;
	41	ldiv_t lresult;
	42	div_t result;
	43	uint16_t days, n, leapyear, years;
	44
	45	/* break down timer into whole and fractional parts of 1 day */
	46	days = *timer / 86400UL;
	47	fract = *timer % 86400UL;
	48
	49	/*
	50	Extract hour, minute, and second from the fractional day
	51	*/
	52	lresult = ldiv(fract, 60L);
	53	timeptr->tm_sec = lresult.rem;
	54	result = div(lresult.quot, 60);
	55	timeptr->tm_min = result.rem;
	56	timeptr->tm_hour = result.quot;
	57
	58	/* Determine day of week ( the epoch was a Saturday ) */
	59	n = days + SATURDAY;
	60	n %= 7;
	61	timeptr->tm_wday = n;
	62
	63	/*
	64	* Our epoch year has the property of being at the conjunction of all three 'leap cycles',
65	* 4, 100, and 400 years ( though we can ignore the 400 year cycle in this library).
66	*
67	* Using this property, we can easily 'map' the time stamp into the leap cycles, quickly
68	* deriving the year and day of year, along with the fact of whether it is a leap year.
69	*/
70
71	/* map into a 100 year cycle */
72	lresult = ldiv((long) days, 36525L);
73	years = 100 * lresult.quot;
74
75	/* map into a 4 year cycle */
76	lresult = ldiv(lresult.rem, 1461L);
77	years += 4 * lresult.quot;
78	days = lresult.rem;
79	if (years > 100)
80	days++;
81
82	/*
83	* 'years' is now at the first year of a 4 year leap cycle, which will always be a leap year,
84	* unless it is 100. 'days' is now an index into that cycle.
85	*/
86	leapyear = 1;
87	if (years == 100)
88	leapyear = 0;
89
90	/* compute length, in days, of first year of this cycle */
91	n = 364 + leapyear;
92
93	/*
94	* if the number of days remaining is greater than the length of the
95	* first year, we make one more division.
96	*/
97	if (days > n) {
98	days -= leapyear;
99	leapyear = 0;
100	result = div(days, 365);
101	years += result.quot;
102	days = result.rem;
103	}
104	timeptr->tm_year = 100 + years;
105	timeptr->tm_yday = days;
106
107	/*
108	Given the year, day of year, and leap year indicator, we can break down the
109	month and day of month. If the day of year is less than 59 (or 60 if a leap year), then
110	we handle the Jan/Feb month pair as an exception.
111	*/
112	n = 59 + leapyear;
113	if (days < n) {
114	/* special case: Jan/Feb month pair */
115	result = div(days, 31);
116	timeptr->tm_mon = result.quot;
117	timeptr->tm_mday = result.rem;
118	} else {
119	/*
120	The remaining 10 months form a regular pattern of 31 day months alternating with 30 day
121	months, with a 'phase change' between July and August (153 days after March 1).
122	We proceed by mapping our position into either March-July or August-December.
123	*/
124	days -= n;
125	result = div(days, 153);
126	timeptr->tm_mon = 2 + result.quot * 5;
127
128	/* map into a 61 day pair of months */
129	result = div(result.rem, 61);
130	timeptr->tm_mon += result.quot * 2;
131
132	/* map into a month */
133	result = div(result.rem, 31);
134	timeptr->tm_mon += result.quot;
135	timeptr->tm_mday = result.rem;
136	}
137
138	/*
139	Cleanup and return
140	*/
141	timeptr->tm_isdst = 0; /* gmt is never in DST */
142	timeptr->tm_mday++; /* tm_mday is 1 based */
143
144	}