[z180-stamp.git] / time / week_of_month.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: week_of_month.c 2362 2013-04-26 22:22:46Z swfltek $ */

/*
	Return the week of month, where 'base' represents the starting day.
	In the USA, the week is generally considered to start on Sunday (base = 0),
	while in Europe it is generally considered to be Monday (base = 1).

	Return value ranges from 0 to 5.
*/

#include <time.h>

uint8_t
week_of_month(const struct tm * timestruct, uint8_t base)
{
	int             first, n;

	/* zero base the day of month */
	n = timestruct->tm_mday - 1;

	/* find the first base day of the month (start of week 1) */
	first = 7 + n - timestruct->tm_wday + base;
	first %= 7;

	/* find days since the first week began */
	n = n - first;

	/* if negative, we are in week 0 */
	if (n < 0)
		return 0;

	return n / 7 + 1;

}
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: week_of_month.c 2362 2013-04-26 22:22:46Z swfltek $ */
	30
	31	/*
	32	Return the week of month, where 'base' represents the starting day.
	33	In the USA, the week is generally considered to start on Sunday (base = 0),
	34	while in Europe it is generally considered to be Monday (base = 1).
	35
	36	Return value ranges from 0 to 5.
	37	*/
	38
	39	#include <time.h>
	40
	41	uint8_t
	42	week_of_month(const struct tm * timestruct, uint8_t base)
	43	{
	44	int first, n;
	45
	46	/* zero base the day of month */
	47	n = timestruct->tm_mday - 1;
	48
	49	/* find the first base day of the month (start of week 1) */
	50	first = 7 + n - timestruct->tm_wday + base;
	51	first %= 7;
	52
	53	/* find days since the first week began */
	54	n = n - first;
	55
	56	/* if negative, we are in week 0 */
	57	if (n < 0)
	58	return 0;
	59
	60	return n / 7 + 1;
	61
	62	}