Commits on Feb 2, 2023

1. Fix 32-bit decoding with large dictionary …

   The 32-bit decoder could corrupt the regenerated data by using regular
   offset mode when there were actually long offsets. This is because we
   were only considering the window size in the calculation, not the
   dictionary size. So a large dictionary could allow longer offsets.
   
   Fix this in two ways:
   1. Instead of looking at the window size, look at the total referencable
      bytes in the history buffer. Use this in the comparison instead of
      the window size. Additionally, we were comparing against the wrong
      value, it was too low. Fix that by computing exactly the maximum
      offset for regular sequence decoding.
   2. If it is possible that we have long offsets due to (1), then check
      the offset code decoding table, and if the decoding table's maximum
      number of additional bits is no more than STREAM_ACCUMULATOR_MIN,
      then we can't have long offsets.
   
   This gates us to be using the long offsets decoder only when we are very
   likely to actually have long offsets.
   
   Note that this bug only affects the decoding of the data, and the
   original compressed data, if re-read with a patched decoder, will
   correctly regenerate the orginal data. Except that the encoder also had
   the same issue previously.
   
   This fixes both the open OSS-Fuzz issues.
   
   Credit to OSS-Fuzz

   

   terrelln committed Feb 2, 2023
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