void vcbprintf(
    vcbprintf_callback user_callback, //!< Unknown
    void *user_data,                  //!< Unknown
    const char *fmt,                  //!< The format specified
    va_list argp                      //!< List of parameter values
  ) {
  char buf[32];
  while (*fmt) {
    if (*fmt == '%') {
      fmt++;
      char fmtChar = *fmt++;
      switch (fmtChar) {
      case '0':
      case '1':
      case '2':
      case '3':
      case '4':
      case '5':
      case '6':
      case '7':
      case '8':
      case '9':
      {
        const char *pad = " ";
        if (fmtChar=='0') {
          pad = "0";
          fmtChar = *fmt++;
        }
        int digits = fmtChar - '0';
        int v = va_arg(argp, int);
        if (*fmt=='x') itostr_extra(v, buf, false, 16);
        else { assert('d' == *fmt); itostr(v, buf, 10); }
        fmt++; // skip over 'd'
        int len = (int)strlen(buf);
        while (len < digits) {
          user_callback(pad,user_data);
          len++;
        }
        user_callback(buf,user_data);
        break;
      }
      case 'd': itostr(va_arg(argp, int), buf, 10); user_callback(buf,user_data); break;
      case 'x': itostr_extra(va_arg(argp, int), buf, false, 16); user_callback(buf,user_data); break;
      case 'L': {
        unsigned int rad = 10;
        bool signedVal = true;
        if (*fmt=='x') { rad=16; fmt++; signedVal = false; }
        itostr_extra(va_arg(argp, JsVarInt), buf, signedVal, rad); user_callback(buf,user_data);
      } break;
      case 'f': ftoa_bounded(va_arg(argp, JsVarFloat), buf, sizeof(buf)); user_callback(buf,user_data);  break;
      case 's': user_callback(va_arg(argp, char *), user_data); break;
      case 'c': buf[0]=(char)va_arg(argp, int/*char*/);buf[1]=0; user_callback(buf, user_data); break;
      case 'q':
      case 'v': {
        bool quoted = fmtChar=='q';
        if (quoted) user_callback("\"",user_data);
        JsVar *v = jsvAsString(va_arg(argp, JsVar*), false/*no unlock*/);
        buf[1] = 0;
        if (jsvIsString(v)) {
          JsvStringIterator it;
          jsvStringIteratorNew(&it, v, 0);
          while (jsvStringIteratorHasChar(&it)) {
            buf[0] = jsvStringIteratorGetChar(&it);
            if (quoted) {
              user_callback(escapeCharacter(buf[0]), user_data);
            } else {
              user_callback(buf,user_data);
            }
            jsvStringIteratorNext(&it);
          }
          jsvStringIteratorFree(&it);
          jsvUnLock(v);
        }
        if (quoted) user_callback("\"",user_data);
      } break;
      case 'j': {
        JsVar *v = va_arg(argp, JsVar*);
        jsfGetJSONWithCallback(v, JSON_SOME_NEWLINES | JSON_PRETTY | JSON_SHOW_DEVICES, 0, user_callback, user_data);
        break;
      }
      case 't': {
        JsVar *v = va_arg(argp, JsVar*);
        const char *n = jsvIsNull(v)?"null":jswGetBasicObjectName(v);
        if (!n) n = jsvGetTypeOf(v);
        user_callback(n, user_data);
        break;
      }
      case 'p': jshGetPinString(buf, (Pin)va_arg(argp, int/*Pin*/)); user_callback(buf, user_data); break;
      default: assert(0); return; // eep
      }
    } else {
      buf[0] = *(fmt++);
      buf[1] = 0;
      user_callback(&buf[0], user_data);
    }
  }
}

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.