A-M baby

Task/Haversine-formula/D/haversine-formula.d

@@ -0,0 +1,24 @@
+import std.stdio, std.math;
+
+real haversineDistance(in real dth1, in real dph1,
+                       in real dth2, in real dph2) pure nothrow {
+
+    enum real R = 6371;
+    enum real TO_RAD = PI / 180;
+
+    alias imr = immutable(real);
+    imr ph1d = dph1 - dph2;
+    imr ph1 = ph1d * TO_RAD;
+    imr th1 = dth1 * TO_RAD;
+    imr th2 = dth2 * TO_RAD;
+
+    imr dz = sin(th1) - sin(th2);
+    imr dx = cos(ph1) * cos(th1) - cos(th2);
+    imr dy = sin(ph1) * cos(th1);
+    return asin(sqrt(dx ^^ 2 + dy ^^ 2 + dz ^^ 2) / 2) * 2 * R;
+}
+
+void main() {
+    writefln("Haversine distance: %.1f km",
+             haversineDistance(36.12, -86.67, 33.94, -118.4));
+}