human
Complete the below
def _check_input_st(x_in, n_fft):

    ''''Aux function.'
    '''

Write me a the Python code you requested?
assistant
#Here is the Python code you requested.
    n_times = x_in.shape[(-1)]
    def _is_power_of_two(n):
        return (not ((n > 0) and (n & (n - 1))))
    if ((n_fft is None) or ((not _is_power_of_two(n_fft)) and (n_times > n_fft))):
        n_fft = (2 ** int(math.ceil(math.log(n_times, 2))))
    elif (n_fft < n_times):
        raise ValueError(('n_fft    cannot    be    smaller    than    signal    size.    Got    %s    <    %s.' % (n_fft, n_times)))
    if (n_times < n_fft):
        warn('The    input    signal    is    shorter    ({0})    than    "n_fft"    ({1}).    Applying    zero    padding.'.format(x_in.shape[(-1)], n_fft))
        zero_pad = (n_fft - n_times)
        pad_array = np.zeros((x_in.shape[:(-1)] + (zero_pad,)), x_in.dtype)
        x_in = np.concatenate((x_in, pad_array), axis=(-1))
    else:
        zero_pad = 0
    return (x_in, n_fft, zero_pad)