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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_year.c 2362 2013-04-26 22:22:46Z swfltek $ */ | |
30 | ||
31 | /* | |
32 | Return the week of year, where 'base' represents the first day of the week. | |
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 52. | |
37 | */ | |
38 | ||
39 | #include <time.h> | |
40 | ||
41 | uint8_t | |
42 | week_of_year(const struct tm * timestruct, uint8_t base) | |
43 | { | |
44 | int first, n; | |
45 | ||
46 | /* find the first base day of the year (start of week 1) */ | |
47 | first = 7 + timestruct->tm_yday - timestruct->tm_wday + base; | |
48 | first %= 7; | |
49 | ||
50 | /* find days since that first base day*/ | |
51 | n = timestruct->tm_yday - first; | |
52 | ||
53 | /* if negative, we are in week 0 */ | |
54 | if (n < 0) | |
55 | return 0; | |
56 | ||
57 | return n / 7 + 1; | |
58 | } |