BAN: Update Endiannes API

Add functions to swap endiannes or convert host to big/little endian

This code should be very compiler friendly and should be optimized to
single bswap instruction on x86.

BAN/include/BAN/Endianness.h

@@ -7,20 +7,62 @@
 namespace BAN
 {
 
+	template<integral T>
+	constexpr T swap_endianness(T value)
+	{
+		if constexpr(sizeof(T) == 1)
+			return value;
+		if constexpr(sizeof(T) == 2)
+			return (((value >> 8) & 0xFF) << 0)
+				 | (((value >> 0) & 0xFF) << 8);
+		if constexpr(sizeof(T) == 4)
+			return (((value >> 24) & 0xFF) <<  0)
+				 | (((value >> 16) & 0xFF) <<  8)
+				 | (((value >>  8) & 0xFF) << 16)
+				 | (((value >>  0) & 0xFF) << 24);
+		if constexpr(sizeof(T) == 8)
+			return (((value >> 56) & 0xFF) <<  0)
+				 | (((value >> 48) & 0xFF) <<  8)
+				 | (((value >> 40) & 0xFF) << 16)
+				 | (((value >> 32) & 0xFF) << 24)
+				 | (((value >> 24) & 0xFF) << 32)
+				 | (((value >> 16) & 0xFF) << 40)
+				 | (((value >>  8) & 0xFF) << 48)
+				 | (((value >>  0) & 0xFF) << 56);
+		T result { 0 };
+		for (size_t i = 0; i < sizeof(T); i++)
+			result |= ((value >> (i * 8)) & 0xFF) << ((sizeof(T) - i - 1) * 8);
+		return result;
+	}
+
+	template<integral T>
+	constexpr T host_to_little_endian(T value)
+	{
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+		return value;
+#else
+		return swap_endianness(value);
+#endif
+	}
+
+	template<integral T>
+	constexpr T host_to_big_endian(T value)
+	{
+#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+		return value;
+#else
+		return swap_endianness(value);
+#endif
+	}
+
 	template<integral T>
 	struct LittleEndian
 	{
 		constexpr operator T() const
 		{
-#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
-			return raw;
-#else
-			T result { 0 };
-			for (size_t i = 0; i < sizeof(T); i++)
-				result = (result << 8) | ((raw >> (sizeof(T) - i - 1) * 8) & 0xFF);
-			return result;
-#endif
+			return host_to_little_endian(raw);
 		}
+	private:
 		T raw;
 	};
 
@@ -29,14 +71,7 @@ namespace BAN
 	{
 		constexpr operator T() const
 		{
-#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
-			return raw;
-#else
-			T result { 0 };
-			for (size_t i = 0; i < sizeof(T); i++)
-				result = (result << 8) | ((raw >> (i * 8)) & 0xFF);
-			return result;
-#endif
+			return host_to_big_endian(raw);
 		}
 	private:
 		T raw;