Re: [pdf-devel] Bug in LZW filter?

[Georg Gottleuber]

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On 29.11.2011 08:37, Aleksander Morgado wrote:
> As you probably know already, digesting this algorithm is pretty 
> tough :-) It would be great if you could document all your
> findings already in the source code, so that one can follow both
> the flow and the comments when reading it.

Commented pdf-stm-f-lzw.c is attached.

I'm going to rewrite the encoder to follow the instructions of
ISO32000 strictly. It will look like:

while (!pdf_buffer_eob_p (in) && !pdf_buffer_full_p (out))
  {
    /* accumulate input data */
    st->string.suffix = in->data [in->rp++];
    if (!lzw_dict_find (&st->dict, &st->string))
      {
        /* emit ouput code */
        lzw_buffer_put_code (&st->buffer, st->string.prefix);
        /* create new dict entry */
        lzw_dict_create_entry (&st->dict, &st->string);

        if (st->dict.size - 1 == st->buffer.maxval - st->early_change)
          {
            /* bitsize increase here */
          }
      }
  }

Regards,
Georg
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pdf-stm-f-lzw_commented.c
Description: Text Data