Fast Practical Adaptive Encoding on Large Alphabets

We present two adaptive coding methods that perform especially well on large alphabets like those used in word-level text compression. The first is based on re-indexing a universal codeword set. The more evolved second method assumes that the underlying codeword set can be optimized and re-generated efficiently. Experiments show that this method, using the Binary Mixed-digit codes as an underlying solution, produces about 1% bigger compressed files than the classical Vitter's algorithm adapted to large alphabets, being more than an order of magnitude faster in encoding and decoding.