Implement utf8 encoding and replace std::codecvt with custom code in utf32 <-> utf8 conversions

libs/util/include/psemek/util/unicode.hpp

@@ -11,6 +11,8 @@ namespace psemek::util
 	std::string to_utf8(std::u32string const & str);
 	std::u32string from_utf8(std::string const & str);
 
+	char * append_utf8(char32_t c, char * out);
+
 	struct utf8_iterator
 	{
 		using value_type = char32_t;

libs/util/source/unicode.cpp

@@ -11,16 +11,54 @@ namespace psemek::util
 #pragma clang diagnostic ignored "-Wdeprecated-declarations"
 #endif
 
-	using converter = std::wstring_convert<std::codecvt_utf8<char32_t>, char32_t>;
-
 	std::string to_utf8(std::u32string const & str)
 	{
-		return converter{}.to_bytes(str);
+		std::string result;
+		result.resize(str.size() * 4);
+
+		char * out = result.data();
+		for (char32_t c : str)
+			out = append_utf8(c, out);
+		result.resize(out - result.data());
+
+		return result;
 	}
 
 	std::u32string from_utf8(std::string const & str)
 	{
-		return converter{}.from_bytes(str);
+		std::u32string result;
+		result.reserve(str.size());
+		for (char32_t c : utf8_range(str))
+			result.push_back(c);
+		return result;
+	}
+
+	char * append_utf8(char32_t c, char * out)
+	{
+		if (c < 0x80)
+		{
+			*out++ = c;
+		}
+		else if (c < 0x800)
+		{
+			*out++ = 0b11000000 | (c >> 6);
+			*out++ = 0b10000000 | (c & 0b00111111);
+		}
+		else if (c < 0x10000)
+		{
+			*out++ = 0b11100000 | (c >> 12);
+			*out++ = 0b10000000 | ((c >> 6) & 0b00111111);
+			*out++ = 0b10000000 | (c & 0b00111111);
+		}
+		else
+		{
+			*out++ = 0b11110000 | (c >> 18);
+			*out++ = 0b10000000 | ((c >> 12) & 0b00111111);
+			*out++ = 0b10000000 | ((c >> 6) & 0b00111111);
+			*out++ = 0b10000000 | (c & 0b00111111);
+		}
+
+		return out;
 	}
 
 #ifdef __clang__