I meant that with the bit ordering that DEFLATE has (the root in the LSB), you can't simply add/subtract 1 to each code to get to the next one, because the carry goes the wrong way.

With a normal (ascending) canonical code, e.g. "2 codes of length 3, 2 codes of length 4" becomes

    000
    001
    0100
    0101

when read into a register. With DEFLATE, the same codes would look like

    000
    100
    0010
    1010

so you need to pre-rotate the bits in your lookup table to match.