why is _REENT_SMALL_CHECK_INIT called in _printf_r/printf functions?

[Can Finner]

Hi,
When _REENT_SMALL is defined, functions like _printf_r/printf call
_REENT_SMALL_CHECK_INIT at first.

int
_DEFUN(_printf_r, (ptr, fmt),
       struct _reent *ptr _AND
       const char *fmt _DOTS)
{
  int ret;
  va_list ap;

  _REENT_SMALL_CHECK_INIT (ptr);
  va_start (ap, fmt);
  ret = _vfprintf_r (ptr, _stdout_r (ptr), fmt, ap);
  va_end (ap);
  return ret;
}

I don't understand this very well, since in _vfprintf_r, CHECK_INIT
will be called which calls __sinit too.
The only thing affected is the 2nd argument passed to _vfprintf_r,
which points to a real FILE struct allocated in __sinit if
_REENT_SMALL_CHECK_INIT is called, otherwise it points to
__sf_fake_stdxx. Does this matter? Since CHECK_INIT called in
_vfprintf_r will point fp away from fake_stdxx anyway.

#define CHECK_INIT(ptr, fp) \
  do						\
    {						\
      if ((ptr) && !(ptr)->__sdidinit)		\
	__sinit (ptr);				\
      if ((fp) == (FILE *)&__sf_fake_stdin)	\
	(fp) = _stdin_r(ptr);			\
      else if ((fp) == (FILE *)&__sf_fake_stdout) \
	(fp) = _stdout_r(ptr);			\
      else if ((fp) == (FILE *)&__sf_fake_stderr) \
	(fp) = _stderr_r(ptr);			\
    }						\
  while (0)


I am not sure if I described my question correctly, please give any
comment you want and I will update the message.

Thanks very much.
-- 
Regards.