facebook
/
zstd
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Clarify special case of offset history update 

If the current sequence has literal length of zero then an offset value
of three is handled in a special manner. While I implemented a golang
decoder I had to consult the educational decoder for clarification on
the update of the offset history in that case. This commit provides the
clarification that the offset value Repeated_Offset1-1 is handled as a
new offset is added to the offset history accordingly.
dev
Ulrich Kunitz 2018-10-22 23:46:43 +02:00
parent ca46afd72b
commit c7942caff0
1 changed files with 4 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
doc/zstd_compression_format.md
View File

@ -919,6 +919,10 @@ This means that when `Repeated_Offset1` (most recent) is used, history is unmodi
When `Repeated_Offset2` is used, it's swapped with `Repeated_Offset1`. When `Repeated_Offset2` is used, it's swapped with `Repeated_Offset1`.
If any other offset is used, it becomes `Repeated_Offset1` and the rest are shift back by one. If any other offset is used, it becomes `Repeated_Offset1` and the rest are shift back by one.
In the case of an `offset_value` of 3 and the literal length of the current
sequence is zero the value `Repeasted_Offset1 - 1_byte` is a new offset,
becoming the lead of the offset history and the first two repeated offsets will
be shifted back.
Skippable Frames Skippable Frames
---------------- ----------------