void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  double d = 0.1;                           // 64 bits double on ESP32 represented with 0x3FB999999999999A in IEEE format
  int64_t n;                                // 64 bits integer
  n = *reinterpret_cast<std::int64_t*>(&d); // attempting to copy the 8 bytes from our double into our integer by dereferencing a pointer ➜  Undefined behavior
  Serial.print("n = 0x");
  Serial.println(n, HEX);

  memcpy(&n, &d, sizeof d);                 // attempting to copy the 8 bytes from our double into our integer with memcpy ➜ fine
  Serial.print("n = 0x");
  Serial.println(n, HEX);
}

void loop() {}