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Status: Verified (2)

RFC 8878, "Zstandard Compression and the 'application/zstd' Media Type", February 2021

Source of RFC: IETF - NON WORKING GROUP

Errata ID: 6441
Status: Verified
Type: Technical
Publication Format(s) : TEXT, PDF, HTML

Reported By: Felix Handte
Date Reported: 2021-02-25
Verifier Name: Barry Leiba
Date Verified: 2021-03-08

Section Appendix A says:

A.1.  Literals Length Code Table

                +=======+========+================+======+
                | State | Symbol | Number_Of_Bits | Base |
                +=======+========+================+======+
                |   0   |   0    |       0        |  0   |
                +-------+--------+----------------+------+
                |   0   |   0    |       4        |  0   |
                +-------+--------+----------------+------+
[...]

A.2.  Match Length Code Table

                +=======+========+================+======+
                | State | Symbol | Number_Of_Bits | Base |
                +=======+========+================+======+
                |   0   |   0    |       0        |  0   |
                +-------+--------+----------------+------+
                |   0   |   0    |       6        |  0   |
                +-------+--------+----------------+------+

[...]

A.3.  Offset Code Table

                +=======+========+================+======+
                | State | Symbol | Number_Of_Bits | Base |
                +=======+========+================+======+
                |   0   |   0    |       0        |  0   |
                +-------+--------+----------------+------+
                |   0   |   0    |       5        |  0   |
                +-------+--------+----------------+------+

It should say:

A.1.  Literals Length Code Table

                +=======+========+================+======+
                | State | Symbol | Number_Of_Bits | Base |
                +=======+========+================+======+
                |   0   |   0    |       4        |  0   |
                +-------+--------+----------------+------+
[...]

A.2.  Match Length Code Table

                +=======+========+================+======+
                | State | Symbol | Number_Of_Bits | Base |
                +=======+========+================+======+
                |   0   |   0    |       6        |  0   |
                +-------+--------+----------------+------+

[...]

A.3.  Offset Code Table

                +=======+========+================+======+
                | State | Symbol | Number_Of_Bits | Base |
                +=======+========+================+======+
                |   0   |   0    |       5        |  0   |
                +-------+--------+----------------+------+

Notes:

Each of the three tables in Appendix A contain two entries for state 0, the first of which in each case incorrectly reports the Number_Of_Bits as 0. The all-zero rows should be removed.

Errata ID: 6442
Status: Verified
Type: Technical
Publication Format(s) : TEXT, PDF, HTML

Reported By: Felix Handte
Date Reported: 2021-02-25
Verifier Name: Barry Leiba
Date Verified: 2021-03-08

Section 3.1.1.5 says:

   The following table shows the values of the Repeated_Offsets as a
   series of sequences are applied to them:

   +=======+==========+===========+===========+===========+============+
   |offset_|literals_ | Repeated_ | Repeated_ | Repeated_ |Comment     |
   | value |  length  |  Offset1  |  Offset2  |  Offset3  |            |
   +=======+==========+===========+===========+===========+============+
   |       |          |     1     |     4     |     8     |starting    |
   |       |          |           |           |           |values      |
   +-------+----------+-----------+-----------+-----------+------------+
   |   1114|    11    |    1111   |     1     |     4     |non-repeat  |
   +-------+----------+-----------+-----------+-----------+------------+
   |      1|    22    |    1111   |     1     |     4     |repeat 1; no|
   |       |          |           |           |           |change      |
   +-------+----------+-----------+-----------+-----------+------------+
   |   2225|    22    |    2222   |    1111   |     1     |non-repeat  |
   +-------+----------+-----------+-----------+-----------+------------+
   |   1114|   111    |    1111   |    2222   |    1111   |non-repeat  |
   +-------+----------+-----------+-----------+-----------+------------+
   |   3336|    33    |    3333   |    1111   |    2222   |non-repeat  |
   +-------+----------+-----------+-----------+-----------+------------+
   |      2|    22    |    1111   |    3333   |    2222   |repeat 2;   |
   |       |          |           |           |           |swap 1 & 2  |
   +-------+----------+-----------+-----------+-----------+------------+
   |      3|    33    |    2222   |    1111   |    3333   |repeat 3;   |
   |       |          |           |           |           |rotate 3 to |
   |       |          |           |           |           |1           |
   +-------+----------+-----------+-----------+-----------+------------+
   |      1|    0     |    2221   |    2222   |    1111   |insert      |
   |       |          |           |           |           |resolved    |
   |       |          |           |           |           |offset      |
   +-------+----------+-----------+-----------+-----------+------------+
   |      1|    0     |    2222   |    2221   |    3333   |repeat 2    |
   +-------+----------+-----------+-----------+-----------+------------+

                         Table 18: Repeated_Offsets

It should say:

   The following table shows the values of the Repeated_Offsets as a
   series of sequences are applied to them:

   +=======+==========+===========+===========+===========+============+
   |offset_|literals_ | Repeated_ | Repeated_ | Repeated_ |Comment     |
   | value |  length  |  Offset1  |  Offset2  |  Offset3  |            |
   +=======+==========+===========+===========+===========+============+
   |       |          |     1     |     4     |     8     |starting    |
   |       |          |           |           |           |values      |
   +-------+----------+-----------+-----------+-----------+------------+
   |   1114|    11    |    1111   |     1     |     4     |non-repeat  |
   +-------+----------+-----------+-----------+-----------+------------+
   |      1|    22    |    1111   |     1     |     4     |repeat 1; no|
   |       |          |           |           |           |change      |
   +-------+----------+-----------+-----------+-----------+------------+
   |   2225|    22    |    2222   |    1111   |     1     |non-repeat  |
   +-------+----------+-----------+-----------+-----------+------------+
   |   1114|   111    |    1111   |    2222   |    1111   |non-repeat  |
   +-------+----------+-----------+-----------+-----------+------------+
   |   3336|    33    |    3333   |    1111   |    2222   |non-repeat  |
   +-------+----------+-----------+-----------+-----------+------------+
   |      2|    22    |    1111   |    3333   |    2222   |repeat 2;   |
   |       |          |           |           |           |swap 1 & 2  |
   +-------+----------+-----------+-----------+-----------+------------+
   |      3|    33    |    2222   |    1111   |    3333   |repeat 3;   |
   |       |          |           |           |           |rotate 3 to |
   |       |          |           |           |           |1           |
   +-------+----------+-----------+-----------+-----------+------------+
   |      3|    0     |    2221   |    2222   |    1111   |insert      |
   |       |          |           |           |           |resolved    |
   |       |          |           |           |           |offset      |
   +-------+----------+-----------+-----------+-----------+------------+
   |      1|    0     |    2222   |    2221   |    3333   |repeat 2    |
   +-------+----------+-----------+-----------+-----------+------------+

                         Table 18: Repeated_Offsets

Notes:

The offset_value in the second-to-last line in the table should be 3, not 1. This line intends to demonstrate the property described earlier in the section that when the sequence's literals_length is 0, an offset_value of 3 resolves to Repeated_Offset1 - 1 and is inserted at the head of the Repeated_Offsets. This is the behavior that is reflected in the rest of the row, which an offset_value of 1 would not trigger (the resolved offset would be 2222, not 2221, and the Repeated_Offsets would remain unchanged, as demonstrated in the 3rd row of the table).

(I wrote this table and it read 3 in the version I provided to the document authors--a typo was introduced somewhere.)

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