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

[Georg Gottleuber]

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On 27.10.2011 10:23, Georg Gottleuber wrote:
>>> -          if (st->buffer.maxval - st->early_change ==
>>> st->dict.size) +          if (st->buffer.maxval -
>>> st->early_change + 2 == st->dict.size) { if
>>> (!lzw_buffer_inc_bitsize (&st->buffer)) {
> 
> I found a very good explanation for a "+1" at this place (a second
> +1 is of course still missing).

I have found the second +1

It is caused by mixing st->dict.size with table entry content:
ISO-32000 says: "The first output code that is 10 bits long shall be
the one following the creation of table entry 511"
(entry 511, not dict.size = 511)

If we create table entry in function lzw_dict_add with:
  d->table[d->size++] = *s;

dict.size is already 511 after the entry of 510. So we have test
against st->dict.size-1 (or add 1 to maxval)

Regards,
Georg
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