return b.exp == event.NoExperiment && len(b.data) > 0 && event.Type(b.data[0]) == go122.EvFrequency
}

// readBatch reads the next full batch from r.
func readBatch(r interface {
	io.Reader
	io.ByteReader
}) (batch, uint64, error) {
	// Read batch header byte.
	b, err := r.ReadByte()
	if err != nil {
		return batch{}, 0, err
	}
	if typ := event.Type(b); typ != go122.EvEventBatch && typ != go122.EvExperimentalBatch {

			// Get next bit - fast path.
			br.bits--
			bit = uint16(br.n>>(br.bits&63)) & 1
		} else {
			// Get next bit - slow path.
			// Use ReadBits to retrieve a single bit
			// from the underling io.ByteReader.
			bit = uint16(br.ReadBits(1))
		}

		// Trick a compiler into generating conditional move instead of branch,
		// by making both loads unconditional.
		l, r := node.left, node.right

		if bit == 1 {