Cet assombrissement est soumis au nom de Paris.pm canal assombri.

By now, you already know what this does. It is a Huffman decompressor.

As always, $/ is first undefined. Then we fetch the length of the compressed data, and the concatenation of the encoded tree and the compressed data (plus the padding). See hfm.pl to see how to create compressed data.

The r subroutine take a two character long string (which m/^[01]{2}$/), splits it and follows the Huffman tree structure (taking the next 8 bits when a leaf (i.e. a character) is needed). If we have not reached a leaf, then the subroutine is called recursively, until the whole tree has been traversed.

$r is a regular expression that will be used to replace any string of 0's and 1's by the corresponding character in the Huffman tree. Please note that we sort the strings in the regular expression so that mismatch is impossible.

After the substition is done, $_ is printed.