(svn r11312) -Codechange: implement a overflow safe integer and use that for money and don't misuses CommandCost to have a overflow safe integer. Based on a patch by Noldo.

12 files changed, 164 insertions, 39 deletions

diff --git a/src/ai/trolly/trolly.cpp b/src/ai/trolly/trolly.cpp
index 2c30b682e..a65371368 100644
--- a/src/ai/trolly/trolly.cpp
+++ b/src/ai/trolly/trolly.cpp
@@ -954,7 +954,7 @@ static void AiNew_State_VerifyRoute(Player *p)
 	//  Check if we have enough money for it!
 	if (p->ainew.new_cost > p->player_money - AI_MINIMUM_MONEY) {
 		// Too bad..
-		DEBUG(ai, 1, "Insufficient funds to build route (%d)", p->ainew.new_cost);
+		DEBUG(ai, 1, "Insufficient funds to build route (%" OTTD_PRINTF64 "d)", (int64)p->ainew.new_cost);
 		p->ainew.state = AI_STATE_NOTHING;
 		return;
 	}
@@ -1086,7 +1086,7 @@ static void AiNew_State_BuildPath(Player *p)
 			}
 		}
 
-		DEBUG(ai, 1, "Finished building path, cost: %d", p->ainew.new_cost);
+		DEBUG(ai, 1, "Finished building path, cost: %" OTTD_PRINTF64 "d", (int64)p->ainew.new_cost);
 		p->ainew.state = AI_STATE_BUILD_DEPOT;
 	}
 }
diff --git a/src/build_vehicle_gui.cpp b/src/build_vehicle_gui.cpp
index bd4938111..38b74cbb8 100644
--- a/src/build_vehicle_gui.cpp
+++ b/src/build_vehicle_gui.cpp
@@ -226,8 +226,8 @@ static int CDECL TrainEnginePowerVsRunningCostSorter(const void *a, const void *
 		* Because of this, the return value have to be reversed as well and we return b - a instead of a - b.
 		* Another thing is that both power and running costs should be doubled for multiheaded engines.
 		* Since it would be multipling with 2 in both numerator and denumerator, it will even themselves out and we skip checking for multiheaded. */
-	Money va = (rvi_a->running_cost_base * _price.running_rail[rvi_a->running_cost_class]) / max((uint16)1, rvi_a->power);
-	Money vb = (rvi_b->running_cost_base * _price.running_rail[rvi_b->running_cost_class]) / max((uint16)1, rvi_b->power);
+	Money va = (rvi_a->running_cost_base * _price.running_rail[rvi_a->running_cost_class]) / max(1U, (uint)rvi_a->power);
+	Money vb = (rvi_b->running_cost_base * _price.running_rail[rvi_b->running_cost_class]) / max(1U, (uint)rvi_b->power);
 	int r = ClampToI32(vb - va);
 
 	return _internal_sort_order ? -r : r;
diff --git a/src/command.cpp b/src/command.cpp
index 4370f9b19..e2133fe4f 100644
--- a/src/command.cpp
+++ b/src/command.cpp
@@ -677,25 +677,13 @@ CommandCost CommandCost::AddCost(CommandCost ret)
 
 CommandCost CommandCost::AddCost(Money cost)
 {
-	/* Overflow protection */
-	if (cost < 0 && (this->cost + cost) > this->cost) {
-		this->cost = INT64_MIN;
-	} else if (cost > 0 && (this->cost + cost) < this->cost) {
-		this->cost = INT64_MAX;
-	} else  {
-		this->cost += cost;
-	}
+	this->cost += cost;
 	return *this;
 }
 
 CommandCost CommandCost::MultiplyCost(int factor)
 {
-	/* Overflow protection */
-	if (factor != 0 && (INT64_MAX / myabs(factor)) < myabs(this->cost)) {
-		this->cost = (this->cost < 0 == factor < 0) ? INT64_MAX : INT64_MIN;
-	} else {
-		this->cost *= factor;
-	}
+	this->cost *= factor;
 	return *this;
 }
 
diff --git a/src/console_cmds.cpp b/src/console_cmds.cpp
index 22047aaa6..6002da263 100644
--- a/src/console_cmds.cpp
+++ b/src/console_cmds.cpp
@@ -1249,7 +1249,7 @@ DEF_CONSOLE_CMD(ConPlayers)
 
 		GetString(buffer, STR_00D1_DARK_BLUE + _player_colors[p->index], lastof(buffer));
 		IConsolePrintF(8, "#:%d(%s) Company Name: '%s'  Year Founded: %d  Money: %" OTTD_PRINTF64 "d  Loan: %" OTTD_PRINTF64 "d  Value: %" OTTD_PRINTF64 "d  (T:%d, R:%d, P:%d, S:%d) %sprotected",
-			p->index + 1, buffer, npi->company_name, p->inaugurated_year, p->player_money, p->current_loan, CalculateCompanyValue(p),
+			p->index + 1, buffer, npi->company_name, p->inaugurated_year, (int64)p->player_money, (int64)p->current_loan, (int64)CalculateCompanyValue(p),
 			/* trains      */ npi->num_vehicle[0],
 			/* lorry + bus */ npi->num_vehicle[1] + npi->num_vehicle[2],
 			/* planes      */ npi->num_vehicle[3],
diff --git a/src/economy.cpp b/src/economy.cpp
index 188b803e6..084da0c05 100644
--- a/src/economy.cpp
+++ b/src/economy.cpp
@@ -95,7 +95,7 @@ Money CalculateCompanyValue(const Player* p)
 	value.AddCost(-p->current_loan);
 	value.AddCost(p->player_money);
 
-	return max(value.GetCost(), 1LL);
+	return max(value.GetCost(), (Money)1);
 }
 
 /** if update is set to true, the economy is updated with this score
diff --git a/src/engine_gui.cpp b/src/engine_gui.cpp
index efe3b1c8b..f164301fd 100644
--- a/src/engine_gui.cpp
+++ b/src/engine_gui.cpp
@@ -120,7 +120,7 @@ void ShowEnginePreviewWindow(EngineID engine)
 static void DrawTrainEngineInfo(EngineID engine, int x, int y, int maxw)
 {
 	const RailVehicleInfo *rvi = RailVehInfo(engine);
-	uint multihead = (rvi->railveh_type == RAILVEH_MULTIHEAD) ? 1 : 0;
+	int multihead = (rvi->railveh_type == RAILVEH_MULTIHEAD) ? 1 : 0;
 
 	SetDParam(0, (_price.build_railvehicle >> 3) * rvi->base_cost >> 5);
 	SetDParam(2, rvi->max_speed * 10 / 16);
diff --git a/src/graph_gui.cpp b/src/graph_gui.cpp
index 7231ec6f3..31f51f578 100644
--- a/src/graph_gui.cpp
+++ b/src/graph_gui.cpp
@@ -41,8 +41,8 @@ enum {
 };
 
 /* Apparently these don't play well with enums. */
-static const int64 INVALID_DATAPOINT     = INT64_MAX; // Value used for a datapoint that shouldn't be drawn.
-static const uint  INVALID_DATAPOINT_POS = UINT_MAX;  // Used to determine if the previous point was drawn.
+static const OverflowSafeInt64 INVALID_DATAPOINT = INT64_MAX; // Value used for a datapoint that shouldn't be drawn.
+static const uint INVALID_DATAPOINT_POS = UINT_MAX;  // Used to determine if the previous point was drawn.
 
 struct GraphDrawer {
 	uint excluded_data; ///< bitmask of the datasets that shouldn't be displayed.
@@ -70,9 +70,9 @@ struct GraphDrawer {
 
 static void DrawGraph(const GraphDrawer *gw)
 {
-	uint x, y;            ///< Reused whenever x and y coordinates are needed.
-	int64 highest_value;  ///< Highest value to be drawn.
-	int x_axis_offset;    ///< Distance from the top of the graph to the x axis.
+	uint x, y;                       ///< Reused whenever x and y coordinates are needed.
+	OverflowSafeInt64 highest_value; ///< Highest value to be drawn.
+	int x_axis_offset;               ///< Distance from the top of the graph to the x axis.
 
 	/* the colors and cost array of GraphDrawer must accomodate
 	 * both values for cargo and players. So if any are higher, quit */
@@ -515,7 +515,7 @@ static void DeliveredCargoGraphWndProc(Window *w, WindowEvent *e)
 				if (p->is_active) {
 					gd.colors[numd] = _colour_gradient[p->player_color][6];
 					for (int j = gd.num_on_x_axis, i = 0; --j >= 0;) {
-						gd.cost[numd][i] = (j >= p->num_valid_stat_ent) ? INVALID_DATAPOINT : p->old_economy[j].delivered_cargo;
+						gd.cost[numd][i] = (j >= p->num_valid_stat_ent) ? INVALID_DATAPOINT : (OverflowSafeInt64)p->old_economy[j].delivered_cargo;
 						i++;
 					}
 				}
@@ -582,7 +582,7 @@ static void PerformanceHistoryWndProc(Window *w, WindowEvent *e)
 				if (p->is_active) {
 					gd.colors[numd] = _colour_gradient[p->player_color][6];
 					for (int j = gd.num_on_x_axis, i = 0; --j >= 0;) {
-						gd.cost[numd][i] = (j >= p->num_valid_stat_ent) ? INVALID_DATAPOINT : p->old_economy[j].performance_history;
+						gd.cost[numd][i] = (j >= p->num_valid_stat_ent) ? INVALID_DATAPOINT : (OverflowSafeInt64)p->old_economy[j].performance_history;
 						i++;
 					}
 				}
diff --git a/src/helpers.hpp b/src/helpers.hpp
index c3f7f7930..f185eecec 100644
--- a/src/helpers.hpp
+++ b/src/helpers.hpp
@@ -158,4 +158,139 @@ template <typename T> void ToggleBitT(T &t, int bit_index)
 	t = (T)(t ^ ((T)1 << bit_index));
 }
 
+/**
+ * Overflow safe template for integers, i.e. integers that will never overflow
+ * you multiply the maximum value with 2, or add 2, or substract somethng from
+ * the minimum value, etc.
+ * @param T     the type these integers are stored with.
+ * @param T_MAX the maximum value for the integers.
+ * @param T_MIN the minimum value for the integers.
+ */
+template <class T, T T_MAX, T T_MIN>
+class OverflowSafeInt
+{
+private:
+	/** The non-overflow safe backend to store the value in. */
+	T m_value;
+public:
+	OverflowSafeInt() : m_value(0) { }
+
+	OverflowSafeInt(const OverflowSafeInt& other) { this->m_value = other.m_value; }
+	OverflowSafeInt(const int64 int_)             { this->m_value = int_; }
+
+	FORCEINLINE OverflowSafeInt& operator = (const OverflowSafeInt& other) { this->m_value = other.m_value; return *this; }
+
+	FORCEINLINE OverflowSafeInt operator - () const { return OverflowSafeInt(-this->m_value); }
+
+	/**
+	 * Safe implementation of addition.
+	 * @param other the amount to add
+	 * @note when the addition would yield more than T_MAX (or less than T_MIN),
+	 *       it will be T_MAX (respectively T_MIN).
+	 */
+	FORCEINLINE OverflowSafeInt& operator += (const OverflowSafeInt& other)
+	{
+		if ((T_MAX - myabs(other.m_value)) < myabs(this->m_value) &&
+				(this->m_value < 0) == (other.m_value < 0)) {
+			this->m_value = (this->m_value < 0) ? T_MIN : T_MAX ;
+		} else {
+			this->m_value += other.m_value;
+		}
+		return *this;
+	}
+
+	/* Operators for addition and substraction */
+	FORCEINLINE OverflowSafeInt  operator +  (const OverflowSafeInt& other) const { OverflowSafeInt result = *this; result += other; return result; }
+	FORCEINLINE OverflowSafeInt  operator +  (const int              other) const { OverflowSafeInt result = *this; result += (int64)other; return result; }
+	FORCEINLINE OverflowSafeInt  operator +  (const uint             other) const { OverflowSafeInt result = *this; result += (int64)other; return result; }
+	FORCEINLINE OverflowSafeInt& operator -= (const OverflowSafeInt& other)       { return *this += (-other); }
+	FORCEINLINE OverflowSafeInt  operator -  (const OverflowSafeInt& other) const { OverflowSafeInt result = *this; result -= other; return result; }
+	FORCEINLINE OverflowSafeInt  operator -  (const int              other) const { OverflowSafeInt result = *this; result -= (int64)other; return result; }
+	FORCEINLINE OverflowSafeInt  operator -  (const uint             other) const { OverflowSafeInt result = *this; result -= (int64)other; return result; }
+
+	FORCEINLINE OverflowSafeInt& operator ++ (int) { return *this += 1; }
+	FORCEINLINE OverflowSafeInt& operator -- (int) { return *this += -1; }
+
+	/**
+	 * Safe implementation of multiplication.
+	 * @param factor the factor to multiply this with.
+	 * @note when the multiplication would yield more than T_MAX (or less than T_MIN),
+	 *       it will be T_MAX (respectively T_MIN).
+	 */
+	FORCEINLINE OverflowSafeInt& operator *= (const int factor)
+	{
+		if (factor != 0 && (T_MAX / myabs(factor)) < myabs(this->m_value)) {
+			 this->m_value = ((this->m_value < 0) == (factor < 0)) ? T_MAX : T_MIN ;
+		} else {
+			this->m_value *= factor ;
+		}
+		return *this;
+	}
+
+	/* Operators for multiplication */
+	FORCEINLINE OverflowSafeInt operator * (const int64  factor) const { OverflowSafeInt result = *this; result *= factor; return result; }
+	FORCEINLINE OverflowSafeInt operator * (const int    factor) const { OverflowSafeInt result = *this; result *= (int64)factor; return result; }
+	FORCEINLINE OverflowSafeInt operator * (const uint   factor) const { OverflowSafeInt result = *this; result *= (int64)factor; return result; }
+	FORCEINLINE OverflowSafeInt operator * (const uint16 factor) const { OverflowSafeInt result = *this; result *= (int64)factor; return result; }
+	FORCEINLINE OverflowSafeInt operator * (const byte   factor) const { OverflowSafeInt result = *this; result *= (int64)factor; return result; }
+
+	/* Operators for division */
+	FORCEINLINE OverflowSafeInt& operator /= (const int              divisor)       { this->m_value /= divisor; return *this; }
+	FORCEINLINE OverflowSafeInt  operator /  (const OverflowSafeInt& divisor) const { OverflowSafeInt result = *this; result /= divisor.m_value; return result; }
+	FORCEINLINE OverflowSafeInt  operator /  (const int              divisor) const { OverflowSafeInt result = *this; result /= divisor; return result; }
+	FORCEINLINE OverflowSafeInt  operator /  (const uint             divisor) const { OverflowSafeInt result = *this; result /= (int)divisor; return result; }
+
+	/* Operators for modulo */
+	FORCEINLINE OverflowSafeInt& operator %= (const int  divisor)       { this->m_value %= divisor; return *this; }
+	FORCEINLINE OverflowSafeInt  operator %  (const int  divisor) const { OverflowSafeInt result = *this; result %= divisor; return result; }
+
+	/* Operators for shifting */
+	FORCEINLINE OverflowSafeInt& operator <<= (const int shift)       { this->m_value <<= shift; return *this; }
+	FORCEINLINE OverflowSafeInt  operator <<  (const int shift) const { OverflowSafeInt result = *this; result <<= shift; return result; }
+	FORCEINLINE OverflowSafeInt& operator >>= (const int shift)       { this->m_value >>= shift; return *this; }
+	FORCEINLINE OverflowSafeInt  operator >>  (const int shift) const { OverflowSafeInt result = *this; result >>= shift; return result; }
+
+	/* Operators for (in)equality when comparing overflow safe ints */
+	FORCEINLINE bool operator == (const OverflowSafeInt& other) const { return this->m_value == other.m_value; }
+	FORCEINLINE bool operator != (const OverflowSafeInt& other) const { return !(*this == other); }
+	FORCEINLINE bool operator >  (const OverflowSafeInt& other) const { return this->m_value > other.m_value; }
+	FORCEINLINE bool operator >= (const OverflowSafeInt& other) const { return this->m_value >= other.m_value; }
+	FORCEINLINE bool operator <  (const OverflowSafeInt& other) const { return !(*this >= other); }
+	FORCEINLINE bool operator <= (const OverflowSafeInt& other) const { return !(*this > other); }
+
+	/* Operators for (in)equality when comparing non-overflow safe ints */
+	FORCEINLINE bool operator == (const int other) const { return this->m_value == other; }
+	FORCEINLINE bool operator != (const int other) const { return !(*this == other); }
+	FORCEINLINE bool operator >  (const int other) const { return this->m_value > other; }
+	FORCEINLINE bool operator >= (const int other) const { return this->m_value >= other; }
+	FORCEINLINE bool operator <  (const int other) const { return !(*this >= other); }
+	FORCEINLINE bool operator <= (const int other) const { return !(*this > other); }
+
+	FORCEINLINE operator int64 () const { return this->m_value; }
+};
+
+/* Sometimes we got int64 operator OverflowSafeInt instead of vice versa. Handle that properly */
+template <class T, int64 T_MAX, int64 T_MIN> FORCEINLINE OverflowSafeInt<T, T_MAX, T_MIN> operator + (int64 a, OverflowSafeInt<T, T_MAX, T_MIN> b) { return b + a; }
+template <class T, int64 T_MAX, int64 T_MIN> FORCEINLINE OverflowSafeInt<T, T_MAX, T_MIN> operator - (int64 a, OverflowSafeInt<T, T_MAX, T_MIN> b) { return -b + a; }
+template <class T, int64 T_MAX, int64 T_MIN> FORCEINLINE OverflowSafeInt<T, T_MAX, T_MIN> operator * (int64 a, OverflowSafeInt<T, T_MAX, T_MIN> b) { return b * a; }
+template <class T, int64 T_MAX, int64 T_MIN> FORCEINLINE OverflowSafeInt<T, T_MAX, T_MIN> operator / (int64 a, OverflowSafeInt<T, T_MAX, T_MIN> b) { return (OverflowSafeInt<T, T_MAX, T_MIN>)a / (int)b; }
+
+/* Sometimes we got int operator OverflowSafeInt instead of vice versa. Handle that properly */
+template <class T, int64 T_MAX, int64 T_MIN> FORCEINLINE OverflowSafeInt<T, T_MAX, T_MIN> operator + (int   a, OverflowSafeInt<T, T_MAX, T_MIN> b) { return b + a; }
+template <class T, int64 T_MAX, int64 T_MIN> FORCEINLINE OverflowSafeInt<T, T_MAX, T_MIN> operator - (int   a, OverflowSafeInt<T, T_MAX, T_MIN> b) { return -b + a; }
+template <class T, int64 T_MAX, int64 T_MIN> FORCEINLINE OverflowSafeInt<T, T_MAX, T_MIN> operator * (int   a, OverflowSafeInt<T, T_MAX, T_MIN> b) { return b * a; }
+template <class T, int64 T_MAX, int64 T_MIN> FORCEINLINE OverflowSafeInt<T, T_MAX, T_MIN> operator / (int   a, OverflowSafeInt<T, T_MAX, T_MIN> b) { return (OverflowSafeInt<T, T_MAX, T_MIN>)a / (int)b; }
+
+/* Sometimes we got uint operator OverflowSafeInt instead of vice versa. Handle that properly */
+template <class T, int64 T_MAX, int64 T_MIN> FORCEINLINE OverflowSafeInt<T, T_MAX, T_MIN> operator + (uint  a, OverflowSafeInt<T, T_MAX, T_MIN> b) { return b + a; }
+template <class T, int64 T_MAX, int64 T_MIN> FORCEINLINE OverflowSafeInt<T, T_MAX, T_MIN> operator - (uint  a, OverflowSafeInt<T, T_MAX, T_MIN> b) { return -b + a; }
+template <class T, int64 T_MAX, int64 T_MIN> FORCEINLINE OverflowSafeInt<T, T_MAX, T_MIN> operator * (uint  a, OverflowSafeInt<T, T_MAX, T_MIN> b) { return b * a; }
+template <class T, int64 T_MAX, int64 T_MIN> FORCEINLINE OverflowSafeInt<T, T_MAX, T_MIN> operator / (uint  a, OverflowSafeInt<T, T_MAX, T_MIN> b) { return (OverflowSafeInt<T, T_MAX, T_MIN>)a / (int)b; }
+
+/* Sometimes we got byte operator OverflowSafeInt instead of vice versa. Handle that properly */
+template <class T, int64 T_MAX, int64 T_MIN> FORCEINLINE OverflowSafeInt<T, T_MAX, T_MIN> operator + (byte  a, OverflowSafeInt<T, T_MAX, T_MIN> b) { return b + a; }
+template <class T, int64 T_MAX, int64 T_MIN> FORCEINLINE OverflowSafeInt<T, T_MAX, T_MIN> operator - (byte  a, OverflowSafeInt<T, T_MAX, T_MIN> b) { return -b + a; }
+template <class T, int64 T_MAX, int64 T_MIN> FORCEINLINE OverflowSafeInt<T, T_MAX, T_MIN> operator * (byte  a, OverflowSafeInt<T, T_MAX, T_MIN> b) { return b * a; }
+template <class T, int64 T_MAX, int64 T_MIN> FORCEINLINE OverflowSafeInt<T, T_MAX, T_MIN> operator / (byte  a, OverflowSafeInt<T, T_MAX, T_MIN> b) { return (OverflowSafeInt<T, T_MAX, T_MIN>)a / (int)b; }
+
 #endif /* HELPERS_HPP */
diff --git a/src/openttd.h b/src/openttd.h
index 5514c2165..2fdf8e0a9 100644
--- a/src/openttd.h
+++ b/src/openttd.h
@@ -69,7 +69,9 @@ typedef uint16 SignID;
 typedef uint16 GroupID;
 typedef uint16 EngineRenewID;
 typedef uint16 DestinationID;
-typedef int64 Money;
+
+typedef OverflowSafeInt<int64, INT64_MAX, INT64_MIN> OverflowSafeInt64;
+typedef OverflowSafeInt64 Money;
 
 /* DestinationID must be at least as large as every these below, because it can
  * be any of them
diff --git a/src/rail_cmd.cpp b/src/rail_cmd.cpp
index 973737db1..00f397453 100644
--- a/src/rail_cmd.cpp
+++ b/src/rail_cmd.cpp
@@ -267,7 +267,7 @@ static CommandCost CheckRailSlope(Slope tileh, TrackBits rail_bits, TrackBits ex
 	   ) return_cmd_error(STR_1000_LAND_SLOPED_IN_WRONG_DIRECTION);
 
 	Foundation f_old = GetRailFoundation(tileh, existing);
-	return CommandCost(f_new != f_old ? _price.terraform : 0);
+	return CommandCost(f_new != f_old ? _price.terraform : (Money)0);
 }
 
 /* Validate functions for rail building */
diff --git a/src/road_cmd.cpp b/src/road_cmd.cpp
index 6d3669925..1b404a97f 100644
--- a/src/road_cmd.cpp
+++ b/src/road_cmd.cpp
@@ -366,7 +366,7 @@ static CommandCost CheckRoadSlope(Slope tileh, RoadBits* pieces, RoadBits existi
 
 	/* foundation is used. Whole tile is leveled up */
 	if ((~_valid_tileh_slopes_road[1][tileh] & road_bits) == ROAD_NONE) {
-		return CommandCost(existing != ROAD_NONE ? 0 : _price.terraform);
+		return CommandCost(existing != ROAD_NONE ? (Money)0 : _price.terraform);
 	}
 
 	/* Force straight roads. */
diff --git a/src/strings.cpp b/src/strings.cpp
index a82bdd15a..393f45f11 100644
--- a/src/strings.cpp
+++ b/src/strings.cpp
@@ -331,15 +331,15 @@ static char *FormatTinyDate(char *buff, Date date, const char* last)
 
 static char *FormatGenericCurrency(char *buff, const CurrencySpec *spec, Money number, bool compact, const char* last)
 {
-	const char* multiplier = "";
+	/* We are going to make number absolute for printing, so
+	 * keep this piece of data as we need it later on */
+	bool negative = number < 0;
+	const char *multiplier = "";
 	char buf[40];
-	char* p;
+	char *p;
 	int j;
 
-	/* Multiply by exchange rate, but do it safely. */
-	CommandCost cs(number);
-	cs.MultiplyCost(spec->rate);
-	number = cs.GetCost();
+	number *= spec->rate;
 
 	/* convert from negative */
 	if (number < 0) {
@@ -374,7 +374,7 @@ static char *FormatGenericCurrency(char *buff, const CurrencySpec *spec, Money n
 			*--p = spec->separator;
 			j = 3;
 		}
-		*--p = '0' + number % 10;
+		*--p = '0' + (char)(number % 10);
 	} while ((number /= 10) != 0);
 	buff = strecpy(buff, p, last);
 
@@ -385,7 +385,7 @@ static char *FormatGenericCurrency(char *buff, const CurrencySpec *spec, Money n
 	 * The only remaining value is 1 (prefix), so everything that is not 0 */
 	if (spec->symbol_pos != 0) buff = strecpy(buff, spec->suffix, last);
 
-	if (cs.GetCost() < 0) {
+	if (negative) {
 		if (buff + Utf8CharLen(SCC_PREVIOUS_COLOUR) > last) return buff;
 		buff += Utf8Encode(buff, SCC_PREVIOUS_COLOUR);
 		*buff = '\0';