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author | Leo C | 2015-06-11 17:43:28 +0200 |
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committer | Leo C | 2015-06-11 17:43:28 +0200 |
commit | 1157e75889d3d6d23d1e2514f401cd5b354bd149 (patch) | |
tree | edad2bcaddaec49a18a1b4bac2b813ce9e5a36bf /time/moon_phase.c | |
parent | 8506d791786eea8ee55db5418a8f646bb2dd3a6d (diff) | |
parent | 057817cb1dc71416bc798b5cd592acfcea87efaa (diff) | |
download | z180-stamp-1157e75889d3d6d23d1e2514f401cd5b354bd149.zip |
Merge branch 'master' into cmdline_edit
Diffstat (limited to 'time/moon_phase.c')
-rw-r--r-- | time/moon_phase.c | 65 |
1 files changed, 65 insertions, 0 deletions
diff --git a/time/moon_phase.c b/time/moon_phase.c new file mode 100644 index 0000000..5fb5826 --- /dev/null +++ b/time/moon_phase.c @@ -0,0 +1,65 @@ +/* + * (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; +} |