1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
|
/*
* (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: moon_phase.c 2365 2013-04-27 15:32:59Z swfltek $ */
/*
Return an approximation to the phase of the moon. Since no attempt is made to account for
Sol, Jupiter or Venus, it will often be off by several hours.
*/
#include <time.h>
#include <math.h>
int8_t
moon_phase(const time_t * timestamp)
{
uint32_t t;
int32_t n;
double mc;
/* refer to first new moon of the epoch */
t = *timestamp - 1744800UL;
/* constrain to 1 lunar cycle */
n = t % 2551443UL;
/* offset by 1/2 lunar cycle */
n -= 1275721L;
mc = n;
mc /= 1275721.0;
mc *= M_PI;
mc = cos(mc) * sin(mc);
mc *= 12.5;
/* scale to range - 100...+ 100 */
n /= 12757L;
n -= mc;
return n;
}
|
