/* * (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. */ /* $Id$ */ /* 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; } }