Convert Unicode to UTF-8

unicode2utf8.cpp

// Convert Unicode to UTF-8
static inline String TinyGsmDecodeHex16bitUTF8(String& instr) {
  String result;
  for (uint16_t i = 0; i < instr.length(); i += 4) {
    char buf[5] = {0,0,0,0,0};
    buf[0] = instr[i];
    buf[1] = instr[i + 1];
    buf[2] = instr[i + 2];
    buf[3] = instr[i + 3];
    uint16_t b = strtol(buf, nullptr, 16);
    if (b < 0x0080) {
      result += char(b);
    } else if (b < 0x0800) {
      result += char(0xC0 | ((b >> 6 ) & 0x1F));
      result += char(0x80 | ( b        & 0x3F));
    } else {
      result += char(0xE0 | ((b >> 12) & 0x0F));
      result += char(0x80 | ((b >> 6 ) & 0x3F));
      result += char(0x80 | ( b        & 0x3F));
    }
    // Ignore 4 byte because 16 bit is use only 3 byte
  }
  return result;
}