switch to avr-libc 1.8.1 time library

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

diff --git a/time/week_of_year.c b/time/week_of_year.c
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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: week_of_year.c 2362 2013-04-26 22:22:46Z swfltek $ */
+
+/*
+       Return the week of year, where 'base' represents the first day of the week.
+       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 52.
+*/
+
+#include <time.h>
+
+uint8_t
+week_of_year(const struct tm * timestruct, uint8_t base)
+{
+       int             first, n;
+
+       /* find the first base day of the year (start of week 1) */
+       first = 7 + timestruct->tm_yday - timestruct->tm_wday + base;
+    first %= 7;
+
+       /* find days since that first base day*/
+       n = timestruct->tm_yday - first;
+
+       /* if negative, we are in week 0 */
+       if (n < 0)
+               return 0;
+
+       return n / 7 + 1;
+}