char top;

#ifdef __arm__

return &top - reinterpret_cast<char*>(sbrk(0));

#elif defined(CORE_TEENSY) || (ARDUINO > 103 && ARDUINO != 151)

return &top - __brkval;

#else // __arm__

return __brkval ? &top - __brkval : &top - __malloc_heap_start;

#endif // __arm__