size_t jsuGetFreeStack() {
#ifdef ARM
  void *frame = __builtin_frame_address(0);
  size_t stackPos = (size_t)((char*)frame);
  size_t stackEnd = (size_t)((char*)&LINKER_END_VAR);
  if (stackPos < stackEnd) return 0; // should never happen, but just in case of overflow!
  return  stackPos - stackEnd;
#elif defined(LINUX)
   char ptr; // this is on the stack
   extern void *STACK_BASE;
   uint32_t count =  (uint32_t)((size_t)STACK_BASE - (size_t)&ptr);
  const uint32_t max_stack = 1000000; // give it 1 megabyte of stack
  if (count>max_stack) return 0;
  return max_stack - count;
 #else
   return 1000000; // no stack depth check on this platform
#endif
}

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.