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use std::convert::TryInto;
use crate::decoding::scratch::FSEScratch;
use crate::decoding::scratch::HuffmanScratch;
use crate::fse::FSETableError;
use crate::huff0::HuffmanTableError;
pub struct Dictionary {
pub id: u32,
pub fse: FSEScratch,
pub huf: HuffmanScratch,
pub dict_content: Vec<u8>,
pub offset_hist: [u32; 3],
}
#[derive(Debug, thiserror::Error)]
#[non_exhaustive]
pub enum DictionaryDecodeError {
#[error(
"Bad magic_num at start of the dictionary; Got: {got:#04X?}, Expected: {MAGIC_NUM:#04x?}"
)]
BadMagicNum { got: [u8; 4] },
#[error(transparent)]
FSETableError(#[from] FSETableError),
#[error(transparent)]
HuffmanTableError(#[from] HuffmanTableError),
}
pub const MAGIC_NUM: [u8; 4] = [0x37, 0xA4, 0x30, 0xEC];
impl Dictionary {
/// parses the dictionary and set the tables
/// it returns the dict_id for checking with the frame's dict_id
pub fn decode_dict(raw: &[u8]) -> Result<Dictionary, DictionaryDecodeError> {
let mut new_dict = Dictionary {
id: 0,
fse: FSEScratch::new(),
huf: HuffmanScratch::new(),
dict_content: Vec::new(),
offset_hist: [2, 4, 8],
};
let magic_num: [u8; 4] = raw[..4].try_into().expect("optimized away");
if magic_num != MAGIC_NUM {
return Err(DictionaryDecodeError::BadMagicNum { got: magic_num });
}
let dict_id = raw[4..8].try_into().expect("optimized away");
let dict_id = u32::from_le_bytes(dict_id);
new_dict.id = dict_id;
let raw_tables = &raw[8..];
let huf_size = new_dict.huf.table.build_decoder(raw_tables)?;
let raw_tables = &raw_tables[huf_size as usize..];
let of_size = new_dict.fse.offsets.build_decoder(
raw_tables,
crate::decoding::sequence_section_decoder::OF_MAX_LOG,
)?;
let raw_tables = &raw_tables[of_size..];
let ml_size = new_dict.fse.match_lengths.build_decoder(
raw_tables,
crate::decoding::sequence_section_decoder::ML_MAX_LOG,
)?;
let raw_tables = &raw_tables[ml_size..];
let ll_size = new_dict.fse.literal_lengths.build_decoder(
raw_tables,
crate::decoding::sequence_section_decoder::LL_MAX_LOG,
)?;
let raw_tables = &raw_tables[ll_size..];
let offset1 = raw_tables[0..4].try_into().expect("optimized away");
let offset1 = u32::from_le_bytes(offset1);
let offset2 = raw_tables[4..8].try_into().expect("optimized away");
let offset2 = u32::from_le_bytes(offset2);
let offset3 = raw_tables[8..12].try_into().expect("optimized away");
let offset3 = u32::from_le_bytes(offset3);
new_dict.offset_hist[0] = offset1;
new_dict.offset_hist[1] = offset2;
new_dict.offset_hist[2] = offset3;
let raw_content = &raw_tables[12..];
new_dict.dict_content.extend(raw_content);
Ok(new_dict)
}
}
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