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

Merge pull request #1145 from terrelln/spec

Browse Source 
Clarify what happens when Number_of_Sequences == 0
This commit is contained in:
Yann Collet 2018-05-22 16:21:40 -07:00 committed by GitHub
commit 4a498f03dc
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 2 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
doc/zstd_compression_format.md
View File

@ -603,6 +603,7 @@ Let's call its first byte `byte0`.
- `if (byte0 == 0)` : there are no sequences. - `if (byte0 == 0)` : there are no sequences.
The sequence section stops there. The sequence section stops there.
Decompressed content is defined entirely as Literals Section content. Decompressed content is defined entirely as Literals Section content.
The FSE tables used in `Repeat_Mode` aren't updated.
- `if (byte0 < 128)` : `Number_of_Sequences = byte0` . Uses 1 byte. - `if (byte0 < 128)` : `Number_of_Sequences = byte0` . Uses 1 byte.
- `if (byte0 < 255)` : `Number_of_Sequences = ((byte0-128) << 8) + byte1` . Uses 2 bytes. - `if (byte0 < 255)` : `Number_of_Sequences = ((byte0-128) << 8) + byte1` . Uses 2 bytes.
- `if (byte0 == 255)`: `Number_of_Sequences = byte1 + (byte2<<8) + 0x7F00` . Uses 3 bytes. - `if (byte0 == 255)`: `Number_of_Sequences = byte1 + (byte2<<8) + 0x7F00` . Uses 3 bytes.
@ -631,7 +632,7 @@ They follow the same enumeration :
No distribution table will be present. No distribution table will be present.
- `RLE_Mode` : The table description consists of a single byte. - `RLE_Mode` : The table description consists of a single byte.
This code will be repeated for all sequences. This code will be repeated for all sequences.
- `Repeat_Mode` : The table used in the previous `Compressed_Block` will be used again, - `Repeat_Mode` : The table used in the previous `Compressed_Block` with `Number_of_Sequences > 0` will be used again,
or if this is the first block, table in the dictionary will be used or if this is the first block, table in the dictionary will be used
No distribution table will be present. No distribution table will be present.
Note that this includes `RLE_mode`, so if `Repeat_Mode` follows `RLE_Mode`, the same symbol will be repeated. Note that this includes `RLE_mode`, so if `Repeat_Mode` follows `RLE_Mode`, the same symbol will be repeated.