// literalFreq and offsetFreq, and generates literalEncoding
// and offsetEncoding.
// The number of literal and offset tokens is returned.
func (w *huffmanBitWriter) indexTokens(tokens []token) (numLiterals, numOffsets int) {
	for i := range w.literalFreq {
		w.literalFreq[i] = 0
	}
	for i := range w.offsetFreq {
		w.offsetFreq[i] = 0
	}

	for _, t := range tokens {