Add makefile, and move latlon to a 'tools' directory

helpers/tools/Makefile

@@ -0,0 +1,24 @@
+bin := latlon
+
+CC = gcc
+
+CFLAGS += -Wall
+CFLAGS += -Wextra
+CFLAGS += -Wpedantic
+CFLAGS += -std=c23
+CFLAGS += -O3
+
+LDFLAGS += -lm
+
+PREFIX ?= $(HOME)/.local/share/dzgui
+
+all: $(bin)
+
+install: $(bin)
+	install -Dm 755 $(bin) $(PREFIX)
+
+$(bin): latlon.c
+	$(CC) $(CFLAGS) $^ -o $@ $(LDFLAGS)
+
+clean:
+	rm -f $(bin)

helpers/tools/latlon.c

@@ -0,0 +1,74 @@
+// This small program computes the distance between two points on the Earths
+// surface. The algorithm used for computing is called haversine formula.
+// Source for the algorithm can be found here:
+// https://en.wikipedia.org/wiki/Haversine_formula
+
+#include <math.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+// Earths radius in meters
+#define RADIUS ((12756L / 2.0L) * 1000L)
+
+// PI natural constant
+#define PI 3.1415926536L
+
+// coordinates struct for storing points
+struct Coordinate {
+    double latitude;
+    double longitude;
+};
+
+/**
+ * @brief Calculates a radian value from an angle
+ */
+double radian_from(const double angle) {
+    return (angle * PI) / 180;
+}
+
+/**
+ * @brief Calculate the haversine function from an angle in radian
+ */
+double haversine(const double angle) { return ((1.0L - cos(angle)) / 2); }
+
+/**
+ * @brief Calculate the distance between two coordinates
+ */
+double great_circle_distance(const struct Coordinate a,
+                             const struct Coordinate b) {
+
+    // calculate longitude and latitude differences
+    struct Coordinate diff_coord = {
+        .longitude = a.longitude - b.longitude,
+        .latitude  = a.latitude - b.latitude,
+    };
+
+    // calculate haversine(theta) value, where theta is the angle between the
+    // two coordinates
+    double hav_theta = haversine(diff_coord.latitude)
+                       + cos(a.latitude) * cos(b.latitude) * haversine(diff_coord.longitude);
+
+    // calculate distance from radius, and haversine(theta) values 
+    double distance = 2 * RADIUS * asin(sqrt(hav_theta));
+
+    return distance;
+}
+
+int main(int argc, const char* argv[]) {
+    if (argc < 5 || argc > 5) {
+        return 1;
+    }
+
+    const struct Coordinate a = {
+        .latitude  = radian_from(atof(argv[1])),
+        .longitude = radian_from(atof(argv[2])),
+    };
+    const struct Coordinate b = {
+        .latitude  = radian_from(atof(argv[3])),
+        .longitude = radian_from(atof(argv[4])),
+    };
+
+    printf("%.1f\n", great_circle_distance(a, b));
+
+    return 0;
+}