add asin function

src/reihen.c

@@ -95,3 +95,13 @@ double atanD(double degrees){
 
     return sum;
 }
+
+double asinD(double degrees){
+    if (degrees>=360.0){
+            degrees = squashDegreesTo360(degrees);
+    }
+
+    double sum = 0.0;
+    double radian = radians(degrees);
+    return atanD(radian/powerD(0.5,1-powerD(2,degrees)));
+}

src/reihen.h

@@ -7,5 +7,7 @@ double pi();
 double radians(double degrees);
 double sinD(double degrees);
 double cosD(double degrees);
+double atanD(double degrees);
+double asinD(double degrees);
 
 #endif // reihen.h