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Use "Insert Count" rather than "Largest Reference" #2111

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merged 14 commits into from Jan 10, 2019
Merged

Use "Insert Count" rather than "Largest Reference" #2111

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79f819f
Use "Insert Count" rather than "Largest Reference"
martinthomson Dec 11, 2018
3da4d1f
Some editorial changes
martinthomson Dec 31, 2018
3a43469
Base editorial changes
martinthomson Dec 31, 2018
9ccc5ca
Text format description for header block prefix
martinthomson Dec 31, 2018
c6296d4
Change absolute indices to 0-based too
martinthomson Dec 31, 2018
39f9930
>=Base
martinthomson Dec 31, 2018
7654602
Mike's comments
martinthomson Jan 7, 2019
21199c4
Drop the 'maybe later'
martinthomson Jan 8, 2019
bcca2eb
the Base, fix some off-by-one errors
martinthomson Jan 9, 2019
7281fc2
More off-by-one errors
martinthomson Jan 10, 2019
43a826c
Insert Count Delta for the Table State Synchronize instruction
martinthomson Jan 10, 2019
8d8f334
Merge branch 'master' into insert-count
martinthomson Jan 10, 2019
6077a99
Use Insert Count Increment rather than Table State Synchronize
martinthomson Jan 10, 2019
f35caef
a -> an
afrind Jan 10, 2019
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30 changes: 14 additions & 16 deletions draft-ietf-quic-qpack.md
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Expand Up @@ -452,14 +452,14 @@ referenced by a given relative index will change while interpreting instructions
on the encoder stream.

~~~~~ drawing
+---+---------------+-----------+
| n | ... | d | Absolute Index
+ - +---------------+ - - - - - +
| 0 | ... | n - d - 1 | Relative Index
+---+---------------+-----------+
^ |
| V
Insertion Point Dropping Point
+-----+---------------+-------+
| n-1 | ... | d | Absolute Index
+ - - +---------------+ - - - +
| 0 | ... | n-d-1 | Relative Index
+-----+---------------+-------+
^ |
| V
Insertion Point Dropping Point

n = count of entries inserted
d = count of entries dropped
Expand All @@ -475,7 +475,7 @@ The Base is encoded as a value relative to the Required Insert Count. The Base
identifies which dynamic table entries can be referenced using relative
indexing, starting with 0 at the last entry added.

Post-base references are used for entries inserted after base, starting at 0 for
Post-Base references are used for entries inserted after base, starting at 0 for
the first entry added after Base, see {{post-base}}.

~~~~~ drawing
Expand Down Expand Up @@ -802,7 +802,7 @@ streams emit the headers for an HTTP request or response.

### Header Block Prefix {#header-prefix}

Each header block is prefixed with two integers. The Required Insert Count
Each header block is prefixed with two integers. The Required Insert Count is
encoded as an integer with an 8-bit prefix after the encoding described in
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{{ric}}). The Base is encoded as sign-and-modulus integer, using a single sign
bit and a value with a 7-bit prefix (see {{base}}).
Expand Down Expand Up @@ -850,7 +850,8 @@ decoder (see {{maximum-table-size}}).


The decoder reconstructs the Required Insert Count using the following
algorithm:
algorithm, where TotalNumberOfInserts is the total number of inserts into the
decoder's dynamic table:

~~~
if EncodedInsertCount == 0:
Expand All @@ -869,9 +870,7 @@ algorithm:
ReqInsertCount += TotalNumberOfInserts - CurrentWrapped
~~~

Where TotalNumberOfInserts is the total number of inserts into the decoder's
dynamic table. This encoding limits the length of the prefix on long-lived
connections.
This encoding limits the length of the prefix on long-lived connections.

For example, if the dynamic table is 100 bytes, then the Required Insert Count
will be encoded modulo 6. If a decoder has received 10 inserts, then an encoded
Expand Down Expand Up @@ -908,8 +907,7 @@ Required Insert Count and Base to the same value. In such case, both the sign
bit and the Delta Base will be set to zero.

A header block that does not reference the dynamic table can use any value for
Base; setting both Required Insert Count and Delta Base to zero is the most
efficient encoding.
Base; setting Delta Base to zero is the most efficient encoding.

For example, with an Required Insert Count of 9, a decoder receives a S bit of 1
and a Delta Base of 2. This sets the Base to 6 and enables post-base indexing
Expand Down