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Avoid having multiple ways to encode Delta Base Index of zero #2005

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Dec 4, 2018
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Avoid having multiple ways to encode Delta Base Index of zero #2005

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Avoid having multiple ways to encode Delta Base Index of zero.
kazuho Nov 14, 2018
57d04bf
Merge branch 'master' into kazuho/delta-base-index-canonical
kazuho Dec 3, 2018
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8 changes: 3 additions & 5 deletions draft-ietf-quic-qpack.md
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Original file line number Diff line number Diff line change
Expand Up @@ -858,7 +858,7 @@ indicates that the Base Index is less than the Largest Reference. That is:
if sign == 0:
baseIndex = largestReference + deltaBaseIndex
else:
baseIndex = largestReference - deltaBaseIndex
baseIndex = largestReference - deltaBaseIndex - 1
~~~

A single-pass encoder determines the absolute value of Base Index before
Expand All @@ -870,10 +870,8 @@ not insert any new entries, Base Index will be greater than the Largest
Reference, so the delta will be positive and the sign bit is set to 0.

An encoder that produces table updates before encoding a header block might set
Largest Reference and Base Index to the same value. When Largest Reference and
Base Index are equal, the Delta Base Index is encoded with a zero sign bit. A
sign bit set to 1 when the Delta Base Index is 0 MUST be treated as a decoder
error.
Largest Reference and Base Index to the same value. In such case, both the sign
bit and the Delta Base Index will be set to zero.

A header block that does not reference the dynamic table can use any value for
Base Index; setting both Largest Reference and Base Index to zero is the most
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