  Canonical Huffman code is an optimal prefix-free compression code whose
codewords enumerated in the lexicographical order form a list of binary words
in non-decreasing lengths. Gagie et al. (2015) gave a representation of this
coding capable to encode or decode a symbol in constant worst case time. It
uses $\sigma \lg \ell_{\text{max}} + o(\sigma) + O(\ell_{\text{max}}^2)$ bits
of space, where $\sigma$ and $\ell_{\text{max}}$ are the alphabet size and
maximum codeword length, respectively. We refine their representation to reduce
the space complexity to $\sigma \lg \ell_{\text{max}} (1 + o(1))$ bits while
preserving the constant encode and decode times. Our algorithmic idea can be
applied to any canonical code.
