Struct Dictionary

pub struct Dictionary {
    pub id: u32,
    pub fse: FSEScratch,
    pub huf: HuffmanScratch,
    pub dict_content: Vec<u8>,
    pub offset_hist: [u32; 3],
}

Zstandard includes support for “raw content” dictionaries, that store bytes optionally used during sequence execution.

https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#dictionary-format

Fields

id: u32

A 4 byte value used by decoders to check if they can use the correct dictionary. This value must not be zero.

fse: FSEScratch

A dictionary can contain an entropy table, either FSE or Huffman.

huf: HuffmanScratch

A dictionary can contain an entropy table, either FSE or Huffman.

dict_content: Vec<u8>

The content of a dictionary acts as a “past” in front of data to compress or decompress, so it can be referenced in sequence commands. As long as the amount of data decoded from this frame is less than or equal to Window_Size, sequence commands may specify offsets longer than the total length of decoded output so far to reference back to the dictionary, even parts of the dictionary with offsets larger than Window_Size. After the total output has surpassed Window_Size however, this is no longer allowed and the dictionary is no longer accessible

offset_hist: [u32; 3]

The 3 most recent offsets are stored so that they can be used during sequence execution, see https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#repeat-offsets for more.

Implementations

impl Dictionary

pub fn decode_dict(raw: &[u8]) -> Result<Dictionary, DictionaryDecodeError>

Parses the dictionary from raw and set the tables it returns the dict_id for checking with the frame’s `dict_id``