Fix undefined behaviour when left-shifting negative values by casting to unsigned

This silences warning spam from UndefinedBehaviorSanitizer.

src/core/overflowsafe_type.hpp

@@ -13,6 +13,7 @@
 #define OVERFLOWSAFE_TYPE_HPP
 
 #include "math_func.hpp"
+#include <type_traits>
 
 /**
  * Overflow safe template for integers, i.e. integers that will never overflow
@@ -28,6 +29,7 @@ class OverflowSafeInt
 private:
 	/** The non-overflow safe backend to store the value in. */
 	T m_value;
+	typedef typename std::make_unsigned<T>::type T_unsigned;
 public:
 	OverflowSafeInt() : m_value(0) { }
 
@@ -103,7 +105,7 @@ public:
 	inline OverflowSafeInt  operator %  (const int  divisor) const { OverflowSafeInt result = *this; result %= divisor; return result; }
 
 	/* Operators for shifting */
-	inline OverflowSafeInt& operator <<= (const int shift)       { this->m_value <<= shift; return *this; }
+	inline OverflowSafeInt& operator <<= (const int shift)       { this->m_value = ((T_unsigned) this->m_value) << shift; return *this; }
 	inline OverflowSafeInt  operator <<  (const int shift) const { OverflowSafeInt result = *this; result <<= shift; return result; }
 	inline OverflowSafeInt& operator >>= (const int shift)       { this->m_value >>= shift; return *this; }
 	inline OverflowSafeInt  operator >>  (const int shift) const { OverflowSafeInt result = *this; result >>= shift; return result; }

src/map_func.h

@@ -232,7 +232,7 @@ static inline uint TileY(TileIndex tile)
  */
 static inline TileIndexDiff ToTileIndexDiff(TileIndexDiffC tidc)
 {
-	return (tidc.y << MapLogX()) + tidc.x;
+	return (((uint) tidc.y) << MapLogX()) + tidc.x;
 }
 
 

src/tree_map.h

@@ -166,7 +166,7 @@ static inline uint GetTreeCount(TileIndex t)
 static inline void AddTreeCount(TileIndex t, int c)
 {
 	assert(IsTileType(t, MP_TREES)); // XXX incomplete
-	_m[t].m5 += c << 6;
+	_m[t].m5 += ((uint) c) << 6;
 }
 
 /**

src/zoom_func.h

@@ -24,7 +24,7 @@
 static inline int ScaleByZoom(int value, ZoomLevel zoom)
 {
 	assert(zoom >= 0);
-	return value << zoom;
+	return ((uint) value) << zoom;
 }
 
 /**
@@ -49,7 +49,7 @@ static inline int UnScaleByZoom(int value, ZoomLevel zoom)
 static inline int ScaleByZoomLower(int value, ZoomLevel zoom)
 {
 	assert(zoom >= 0);
-	return value << zoom;
+	return ((uint) value) << zoom;
 }
 
 /**