Adding cspanf to radixmath/util for dealing with periodic intervals

radixmath/tests/tstUtil.cc

@@ -4,6 +4,34 @@
 #include "radixmath/util.hh"
 
 using namespace radix;
+TEST(radix, cspanf)
+{
+    Real lon = -190;
+    Real v = cspanf(lon, -180, 180);
+    EXPECT_FLOAT_EQ(170, v);
+    lon = 190;
+    v = cspanf(lon , -180, 180);
+    EXPECT_FLOAT_EQ(v, -170);
+    lon = 360;
+    v = cspanf(lon , -180, 180);
+    EXPECT_FLOAT_EQ(v, 0);
+    lon = -360;
+    v = cspanf(lon , -180, 180);
+    EXPECT_FLOAT_EQ(v, 0);
+    Real lat = -100;
+    v = cspanf(lat, -90, 90);
+    EXPECT_FLOAT_EQ(80, v);
+    lat = 100;
+    v = cspanf(lat, -90, 90);
+    EXPECT_FLOAT_EQ(-80, v);
+    lat = 180;
+    v = cspanf(lat, -90, 90);
+    EXPECT_FLOAT_EQ(v, 0);
+    lat = -180;
+    v = cspanf(lat, -90, 90);
+    EXPECT_FLOAT_EQ(v, 0);
+}
+
 TEST(radix, greatCircleDistance){
     { // Quadrant 2 north west hemisphere
         double delta = 0.05;

radixmath/util.cc

@@ -152,4 +152,19 @@ Real cylinderVolume(Real r, Real h)
     return (PI * std::pow(r, 2) * h);
 }
 
+Real cspanf(Real value, Real begin, Real end)
+{
+    Real first = 0.0, last = 0.0;
+    first = std::min(begin, end);
+    last = std::max(begin, end);
+    value = std::fmod(value - first,last - first);
+    if(value <= 0)
+    {
+        return value + last;
+    } else
+    {
+        return value + first;
+    }
+}
+
 } // namespace radix

radixmath/util.hh

@@ -16,6 +16,18 @@
 namespace radix
 {
 
+/**
+ * @brief cspanf returns a value in the interval (begin,end]
+ * This function is used to reduce periodic variables to a standard range.
+ * It adjusts for the behaviour of the mod function which provides positive results
+ * for position input and negative results for negative input.
+ * @param value number to be reduced to the span
+ * @param begin first value of the span
+ * @param end last value of the span
+ * @return Real the reduced value
+ */
+Real cspanf(Real value, Real begin, Real end);
+
 /**
  * @brief haversine The Haversine formula for calculating great-circle
  * @param lat1