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/*
* (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: iso_week_date_r.c 2394 2013-05-04 10:26:24Z swfltek $ */
/*
Compute the ISO 8601 week date corresponding to the given year and day of year.
See http://en.wikipedia.org/wiki/ISO_week_date for a full description. To summarize:
Weeks are numbered from 1 to 53.
Week days are numbered 1 to 7, beginning with Monday as day 1.
The first week of the year contains the first Thursday in that year.
Dates prior to week 1 belong to the final week of the previous year.
The final week of the year contains the last Thursday in that year.
Dates after the final week belong to week 1 of the following year.
*/
#include <time.h>
void
iso_week_date_r(int y, int yday, struct week_date * iso)
{
uint16_t years, n, wday;
int weeknum;
int isLeap;
iso->year = y;
isLeap = is_leap_year(y);
/* compute days elapsed since epoch */
years = y - 2000;
n = 365 * years + yday;
if (years) {
n++; /* epoch was a leap year */
n += years / 4;
n -= isLeap;
if (years > 100)
n--;
}
/* compute ISO8601 day of week (1 ... 7, Monday = 1) */
wday = n + 6; /* epoch was a Saturday */
wday %= 7;
if (wday == 0)
wday = 7;
iso->day = wday;
/* compute tentative week number */
weeknum = yday + 11 - wday;
weeknum /= 7;
/* if 53, it could be week 1 of the following year */
if (weeknum == 53) {
/*
The final week must include its Thursday in the year. We determine the yday of this
weeks Thursday, and test whether it exceeds this years length.
*/
/* determine final yday of this year, 364 or 365 */
n = 364 + isLeap;
/* compute yday of this weeks Thursday */
wday--; /* convert to zero based week, Monday = 0 */
yday -= wday; /* yday of this weeks Monday */
yday += 3; /* yday of this weeks Thursday */
/* Is this weeks Thursday included in the year? */
if (yday > (int) n) {
iso->year++;
weeknum = 1;
}
}
iso->week = weeknum;
/*
If zero, it is the final week of the previous year.
We determine that by asking for the week number of Dec 31.
*/
if (weeknum == 0) {
y = y - 1;
iso_week_date_r(y, 364 + is_leap_year(y), iso);
iso->day = wday;
}
}
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