const char fichier[] = R"--(.0|The quick brown fox jumps over the lazy dog
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const size_t hauteurEcran = 5;
size_t ligneDebut = 0;

const char * debut = nullptr;
size_t nombreDeLignes = 0;

size_t compteLignes(const char * s) {
  size_t n = *s == '\0' ? 0 : 1;
  while (*s)
    if ((*s++ == '\n') && (*s != '\0')) n++;
  return n;
}

const char * pointeurDebutLigne(size_t numeroLigne) {
  const char * ptr = debut;
  for (size_t i = 0; i < numeroLigne; i++) {
    while (*ptr && *ptr++ != '\n');
  }
  return ptr;
}

void imprime(size_t numeroLigne) {
  char * ptr = pointeurDebutLigne(numeroLigne);

  for (size_t i = 0; i < hauteurEcran; i++) {
    while (*ptr && *ptr != '\n') Serial.write(*ptr++);
    Serial.write('\n');
    if (*ptr) ptr++;
  }
  Serial.println("----------");
}

void setup() {
  Serial.begin(115200); Serial.println();
  debut = fichier;
  nombreDeLignes = compteLignes(debut);
  if (nombreDeLignes == 0) {
    Serial.println("erreur, fichier vide");
    while (true) yield();
  }
  imprime(ligneDebut);
}

void loop() {
  switch (Serial.read()) {
    case 'u':   // up
      if (ligneDebut > 0) ligneDebut -= 1;;
      imprime(ligneDebut);
      break;
    case 'U':  // page up
      if (ligneDebut >= hauteurEcran) ligneDebut -= hauteurEcran;
      else ligneDebut = 0;
      imprime(ligneDebut);
      break;
    case 'd':   // down
      if (ligneDebut < nombreDeLignes - 1) ligneDebut += 1;;
      imprime(ligneDebut);
      break;
    case 'D':  // page down
      if (ligneDebut < nombreDeLignes - hauteurEcran) ligneDebut += hauteurEcran;
      else ligneDebut = nombreDeLignes - 1;
      imprime(ligneDebut);
      break;
  }
  delay(1);
}