Fix OpenTTD#7561: Fix power/running cost vehicle engine sorter

src/build_vehicle_gui.cpp

@@ -273,21 +273,31 @@ static bool EnginePowerVsRunningCostSorter(const EngineID &a, const EngineID &b)
 	uint p_b = e_b->GetPower();
 	Money r_a = e_a->GetRunningCost();
 	Money r_b = e_b->GetRunningCost();
-	/* Check if running cost is zero in one or both engines */
+	/* Check if running cost is zero in one or both engines.
+	 * If only one of them is zero then that one has higher value,
+	 * else if both have zero cost then compare powers.
+	 */
 	if (r_a == 0) {
 		if (r_b == 0) {
-			if (p_a == p_b) return EngineNumberSorter(a,b);
-			return _engine_sort_direction ? p_a >= p_b : p_a < p_b;
+			/* If it is ambiguous which to return go with their ID */
+			if (p_a == p_b) return EngineNumberSorter(a, b);
+			return _engine_sort_direction != (p_a < p_b);
 		}
 		return !_engine_sort_direction;
 	}
-	if (r_b == 0 ) return _engine_sort_direction;
-
-	float va = p_a / r_a;
-	float vb = p_b / r_b;
-	/* Use EngineID to sort instead since we want consistent sorting */
-	if (va == vb) return EngineNumberSorter(a,b);
-	return _engine_sort_direction ? va > vb : va < vb;
+	if (r_b == 0) return _engine_sort_direction;
+	/* Using double for more precision when comparing close values.
+	 * This shouldn't have any major effects in performance nor in keeping
+	 * the game in sync between players since it's used in GUI only in client side
+	 */
+	double v_a = (double)p_a / (double)r_a;
+	double v_b = (double)p_b / (double)r_b;
+	/* Use EngineID to sort if both have same power/running cost,
+	 * for example if both had zero power,
+	 * since we want consistent sorting
+	 */
+	if (v_a == v_b) return EngineNumberSorter(a, b);
+	return _engine_sort_direction != (v_a < v_b);
 }
 
 /* Train sorting functions */