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implement optional parity contexts

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This commit is contained in:
Dennis Ranke
2022-09-20 23:24:19 +02:00
parent cc41feb5cd
commit f5fc9bd005
5 changed files with 84 additions and 29 deletions
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52
src/lz.rs
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@@ -9,41 +9,49 @@ pub enum Op {
impl Op {
pub fn encode(&self, coder: &mut dyn EntropyCoder, state: &mut CoderState) {
let literal_base = state.pos % state.parity_contexts * 256;
match self {
&Op::Literal(lit) => {
encode_bit(coder, state, 0, false);
encode_bit(coder, state, literal_base, false);
let mut context_index = 1;
for i in (0..8).rev() {
let bit = (lit >> i) & 1 != 0;
encode_bit(coder, state, context_index, bit);
encode_bit(coder, state, literal_base + context_index, bit);
context_index = (context_index << 1) | bit as usize;
}
state.prev_was_match = false;
state.pos += 1;
}
&Op::Match { offset, len } => {
encode_bit(coder, state, 0, true);
encode_bit(coder, state, literal_base, true);
if !state.prev_was_match {
encode_bit(coder, state, 256, offset != state.last_offset);
encode_bit(
coder,
state,
256 * state.parity_contexts,
offset != state.last_offset,
);
} else {
assert!(offset != state.last_offset);
}
if offset != state.last_offset {
encode_length(coder, state, 257, offset + 1);
encode_length(coder, state, 256 * state.parity_contexts + 1, offset + 1);
state.last_offset = offset;
}
encode_length(coder, state, 257 + 64, len);
encode_length(coder, state, 256 * state.parity_contexts + 65, len);
state.prev_was_match = true;
state.pos += len as usize;
}
}
}
}
pub fn encode_eof(coder: &mut dyn EntropyCoder, state: &mut CoderState) {
encode_bit(coder, state, 0, true);
encode_bit(coder, state, state.pos % state.parity_contexts * 256, true);
if !state.prev_was_match {
encode_bit(coder, state, 256, true);
encode_bit(coder, state, 256 * state.parity_contexts, true);
}
encode_length(coder, state, 257, 1);
encode_length(coder, state, 256 * state.parity_contexts + 1, 1);
}
fn encode_bit(
@@ -76,16 +84,20 @@ fn encode_length(
#[derive(Clone)]
pub struct CoderState {
contexts: ContextState,
parity_contexts: usize,
last_offset: u32,
prev_was_match: bool,
pos: usize,
}
impl CoderState {
pub fn new() -> CoderState {
pub fn new(parity_contexts: usize) -> CoderState {
CoderState {
contexts: ContextState::new(1 + 255 + 1 + 64 + 64),
contexts: ContextState::new((1 + 255) * parity_contexts + 1 + 64 + 64),
last_offset: 0,
parity_contexts,
prev_was_match: false,
pos: 0,
}
}
@@ -94,9 +106,9 @@ impl CoderState {
}
}
pub fn unpack(packed_data: &[u8], use_bitstream: bool) -> Vec<u8> {
pub fn unpack(packed_data: &[u8], use_bitstream: bool, parity_contexts: usize) -> Vec<u8> {
let mut decoder = RansDecoder::new(packed_data, use_bitstream);
let mut contexts = ContextState::new(1 + 255 + 1 + 64 + 64);
let mut contexts = ContextState::new((1 + 255) * parity_contexts + 1 + 64 + 64);
let mut result = vec![];
let mut offset = 0;
let mut prev_was_match = false;
@@ -119,14 +131,17 @@ pub fn unpack(packed_data: &[u8], use_bitstream: bool) -> Vec<u8> {
}
loop {
if decoder.decode_with_context(&mut contexts.context_mut(0)) {
if prev_was_match || decoder.decode_with_context(&mut contexts.context_mut(256)) {
offset = decode_length(&mut decoder, &mut contexts, 257) - 1;
let literal_base = result.len() % parity_contexts * 256;
if decoder.decode_with_context(&mut contexts.context_mut(literal_base)) {
if prev_was_match
|| decoder.decode_with_context(&mut contexts.context_mut(256 * parity_contexts))
{
offset = decode_length(&mut decoder, &mut contexts, 256 * parity_contexts + 1) - 1;
if offset == 0 {
break;
}
}
let length = decode_length(&mut decoder, &mut contexts, 257 + 64);
let length = decode_length(&mut decoder, &mut contexts, 256 * parity_contexts + 65);
for _ in 0..length {
result.push(result[result.len() - offset]);
}
@@ -135,7 +150,8 @@ pub fn unpack(packed_data: &[u8], use_bitstream: bool) -> Vec<u8> {
let mut context_index = 1;
let mut byte = 0;
for i in (0..8).rev() {
let bit = decoder.decode_with_context(&mut contexts.context_mut(context_index));
let bit = decoder
.decode_with_context(&mut contexts.context_mut(literal_base + context_index));
context_index = (context_index << 1) | bit as usize;
byte |= (bit as u8) << i;
}