feat: move func to calc package

pkg/calc/map.go

@@ -0,0 +1,20 @@
+package calc
+
+import "math"
+
+// shortest distance between points on torus map
+func ShortDistance(w, h uint32, x1, y1, x2, y2 float64) float64 {
+	return math.Hypot(Deltas(w, h, x1, y1, x2, y2))
+}
+
+func Deltas(w, h uint32, x1, y1, x2, y2 float64) (float64, float64) {
+	dx := math.Abs(x2 - x1)
+	dy := math.Abs(y2 - y1)
+	if dx > float64(w/2) {
+		dx = float64(h) - dx
+	}
+	if dy > float64(h/2) {
+		dy = float64(h) - dy
+	}
+	return dx, dy
+}