switch to avr-libc 1.8.1 time library

1 files changed, 77 insertions, 0 deletions

diff --git a/time/solar_declination.c b/time/solar_declination.c
new file mode 100644
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+++ b/time/solar_declination.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: solar_declination.c 2369 2013-04-28 14:19:35Z swfltek $ */
+
+/*
+    Were it not for the eccentricity of Earths orbit, this would be a trivial function.
+
+    We compute the Earths orbital position with respect to perihelion, from which we derive a
+    'velocity correction factor'. We then compute the orbital angle with respect to the
+    December solstice, as 'modulated' by that correction factor.
+
+    Due to the accumulation of rounding errors, the computed December solstice of 2135 will lag
+    the actual solstice by many hours. A fudge factor, 'LAG', distributes the error across
+    the 136 year range of this library.
+*/
+
+#include <time.h>
+#include <math.h>
+#include "ephemera_common.h"
+
+#define LAG 38520
+
+double
+solar_declination(const time_t * timer)
+{
+
+    uint32_t        fT, oV;
+    double          dV, dT;
+
+    /* Determine orbital angle relative to perihelion of January 1999 */
+    oV = *timer % ANOM_YEAR;
+    oV += PERIHELION;
+    dV = oV;
+    dV /= ANOM_CYCLE;
+
+    /* Derive velocity correction factor from the perihelion angle */
+    dV = sin(dV);
+    dV *= DELTA_V;
+
+    /* Determine orbital angle relative to solstice of December 1999 */
+    fT = *timer % TROP_YEAR;
+    fT += SOLSTICE + LAG;
+    dT = fT;
+    dT /= TROP_CYCLE;
+    dT += dV;
+
+    /* Finally having the solstice angle, we can compute the declination */
+    dT = cos(dT) * INCLINATION;
+
+    return -dT;
+}