def _is_sequence_right_padded(mask):
    """Check the mask tensor and see if it right padded.

    cuDNN uses the sequence length param to skip the tailing
    timestep. If the data is left padded, or not a strict right padding (has
    masked value in the middle of the sequence), then cuDNN won't work
    properly in those cases.

    Left padded data: [[False, False, True, True, True]].
    Right padded data: [[True, True, True, False, False]].
    Mixture of mask/unmasked data: [[True, False, True, False, False]].

    Note that for the mixed data example above, the actually data RNN should see
    are those 2 Trues (index 0 and 2), the index 1 False should be ignored and
    not pollute the internal states.

    Args:
        mask: the Boolean tensor with shape [batch, timestep]

    Returns:
        boolean scalar tensor, whether the mask is strictly right padded.
    """
    max_seq_length = tf.shape(mask)[1]
    count_of_true = tf.reduce_sum(tf.cast(mask, tf.int32), axis=1)
    right_padded_mask = tf.sequence_mask(count_of_true, maxlen=max_seq_length)
    return tf.reduce_all(
        tf.equal(
            tf.cast(mask, dtype="bool"),
            tf.cast(right_padded_mask, dtype="bool"),
        )
    )
Check the mask tensor and see if it right padded.

    cuDNN uses the sequence length param to skip the tailing
    timestep. If the data is left padded, or not a strict right padding (has
    masked value in the middle of the sequence), then cuDNN won't work
    properly in those cases.

    Left padded data: [[False, False, True, True, True]].
    Right padded data: [[True, True, True, False, False]].
    Mixture of mask/unmasked data: [[True, False, True, False, False]].

    Note that for the mixed data example above, the actually data RNN should see
    are those 2 Trues (index 0 and 2), the index 1 False should be ignored and
    not pollute the internal states.

    Args:
        mask: the Boolean tensor with shape [batch, timestep]

    Returns:
        boolean scalar tensor, whether the mask is strictly right padded.
    
keras/src/backend/tensorflow/rnn.py