Function utf8catcodepoint

3rd/utf8/include/utf8.h:1221–1263

}

utf8_int8_t *utf8catcodepoint(utf8_int8_t *str, utf8_int32_t chr, size_t n) {
  if (0 == ((utf8_int32_t)0xffffff80 & chr)) {
    // 1-byte/7-bit ascii
    // (0b0xxxxxxx)
    if (n < 1) {
      return utf8_null;
    }
    str[0] = (utf8_int8_t)chr;
    str += 1;
  } else if (0 == ((utf8_int32_t)0xfffff800 & chr)) {
    // 2-byte/11-bit utf8 code point
    // (0b110xxxxx 0b10xxxxxx)
    if (n < 2) {
      return utf8_null;
    }
    str[0] = (utf8_int8_t)(0xc0 | (utf8_int8_t)((chr >> 6) & 0x1f));
    str[1] = (utf8_int8_t)(0x80 | (utf8_int8_t)(chr & 0x3f));
    str += 2;
  } else if (0 == ((utf8_int32_t)0xffff0000 & chr)) {
    // 3-byte/16-bit utf8 code point
    // (0b1110xxxx 0b10xxxxxx 0b10xxxxxx)
    if (n < 3) {
      return utf8_null;
    }
    str[0] = (utf8_int8_t)(0xe0 | (utf8_int8_t)((chr >> 12) & 0x0f));
    str[1] = (utf8_int8_t)(0x80 | (utf8_int8_t)((chr >> 6) & 0x3f));
    str[2] = (utf8_int8_t)(0x80 | (utf8_int8_t)(chr & 0x3f));
    str += 3;
  } else { // if (0 == ((int)0xffe00000 & chr)) {
    // 4-byte/21-bit utf8 code point
    // (0b11110xxx 0b10xxxxxx 0b10xxxxxx 0b10xxxxxx)
    if (n < 4) {
      return utf8_null;
    }
    str[0] = (utf8_int8_t)(0xf0 | (utf8_int8_t)((chr >> 18) & 0x07));
    str[1] = (utf8_int8_t)(0x80 | (utf8_int8_t)((chr >> 12) & 0x3f));
    str[2] = (utf8_int8_t)(0x80 | (utf8_int8_t)((chr >> 6) & 0x3f));
    str[3] = (utf8_int8_t)(0x80 | (utf8_int8_t)(chr & 0x3f));
    str += 4;
  }

  return str;
}

utf8_constexpr14_impl int utf8islower(utf8_int32_t chr) {
  return chr != utf8uprcodepoint(chr);