static inline bool u8_is_ascii(char c)
{
return !(c & (1 << 7));
}

static inline bool u8_is_noascii_char(char c)
{
return !((c >> 6 & 0x3) ^ 0x2);
}

static inline int u8_is_noascii_head(char c)
{
if (!((c >> 5 & 0x7) ^ 0x6)) return 2;
if (!((c >> 4 & 0xF) ^ 0xE)) return 3;
if (!((c >> 3 & 0x1F) ^ 0x1E)) return 4;
return 0;
}

static inline size_t u8_len(const std::string& str)
{
int _index = 0;
for (int i = 0; i < str.size();) {
char c = str.at(i);
int size = u8_is_noascii_head(c);
if (size > 0) {
i += size;
} else if (u8_is_ascii(c)) {
++i;
} else {
return -1;
}

++_index;
}

return _index;
}


static inline std::string u8_at(const std::string& str, int index)
{
std::string t;
int _index = 0;
for (int i = 0; i < str.size();) {
char c = str.at(i);
int size = u8_is_noascii_head(c);
if (size > 0) {
if (_index == index) {
t.assign(str.begin() + i, str.begin() + i + size);
goto quit;
} else {
i += size;
++_index;
}
continue;
} else if (u8_is_ascii(c)) {
if (_index == index) {
t = std::string(1, c);
goto quit;
} else {
++_index;
}
} else {
goto quit;
}
++i;
}

overflow:
console::error("buffer overflow");
exit(-1);

quit:
return t;
}


static inline std::vector<std::string> u8_each_split(const std::string& str)
{
std::vector<std::string> re;
std::string t;
for (int i = 0; i < str.size();) {
char c = str.at(i);
int size = u8_is_noascii_head(c);
if (size > 0) {
t.clear();
t.assign(str.begin() + i, str.begin() + i + size);
i += size;
re.push_back(t);
continue;
} else if (u8_is_ascii(c)) {
re.push_back(std::string(1, c));
} else {
goto quit;
}
++i;
}
quit:
return re;
}