implement simplified prob update, update unpack.c

asm_unpackers/.gitignore

@@ -1 +0,0 @@
-/build/

asm_unpackers/Makefile

@@ -1,30 +0,0 @@
-build/unpack_riscv64: ../c_unpacker/main.c ../c_unpacker/unpack.c
-	mkdir -p build
-	riscv64-linux-gnu-gcc -g -static -o $@ $^
-
-test_riscv64: build/unpack_riscv64
-	qemu-riscv64 $< test_data.upk /tmp/out.bin
-	cmp test_data.bin /tmp/out.bin
-
-build/unpack_armv6m: ../c_unpacker/main.c unpack_armv6m.S
-	mkdir -p build
-	arm-linux-gnueabihf-gcc -g -static -o $@ $^
-
-test_armv6m: build/unpack_armv6m
-	qemu-arm $< test_data.upk /tmp/out.bin
-	cmp test_data.bin /tmp/out.bin
-
-build/unpack_armv6m.bin: unpack_armv6m.S
-	arm-none-eabi-gcc -march=armv6-m -c -o build/unpack_armv6m.o $?
-	arm-none-eabi-objcopy -O binary --only-section=.text build/unpack_armv6m.o $@
-	
-build/unpack_c: ../c_unpacker/main.c ../c_unpacker/unpack.c
-	mkdir -p build
-	gcc -g -o $@ $^
-
-test_c: build/unpack_c
-	$< test_data.upk /tmp/out.bin
-	cmp test_data.bin /tmp/out.bin
-
-sizes: build/unpack_armv6m.bin
-	ls -l build/*.bin

asm_unpackers/test_data.bin

@@ -1,99 +0,0 @@
-typedef unsigned char u8;
-typedef unsigned short u16;
-typedef unsigned long u32;
-
-u8* upkr_data_ptr;
-u8 upkr_probs[1 + 255 + 1 + 2*32 + 2*32]; 
-#ifdef UPKR_BITSTREAM
-u16 upkr_state;
-u8 upkr_current_byte;
-int upkr_bits_left;
-#else
-u32 upkr_state;
-#endif
-
-int upkr_decode_bit(int context_index) {
-#ifdef UPKR_BITSTREAM
-    while(upkr_state < 32768) {
-        if(upkr_bits_left == 0) {
-            upkr_current_byte = *upkr_data_ptr++;
-            upkr_bits_left = 8;
-        }
-        upkr_state = (upkr_state << 1) + (upkr_current_byte & 1);
-        upkr_current_byte >>= 1;
-        --upkr_bits_left;
-    }
-#else
-    while(upkr_state < 4096) {
-        upkr_state = (upkr_state << 8) | *upkr_data_ptr++;
-    }
-#endif
-   
-    int prob = upkr_probs[context_index];
-    int bit = (upkr_state & 255) < prob ? 1 : 0;
-    
-    int tmp = prob;
-    if(!bit) {
-        tmp = 256 - tmp;
-    }
-    upkr_state = tmp * (upkr_state >> 8) + (upkr_state & 255);
-    tmp += (256 - tmp + 8) >> 4;
-    if(!bit) {
-        upkr_state -= prob;
-        tmp = 256 - tmp;
-    }
-    upkr_probs[context_index] = tmp;
-
-    return bit;
-}
-
-int upkr_decode_length(int context_index) {
-    int length = 0;
-    int bit_pos = 0;
-    while(upkr_decode_bit(context_index)) {
-        length |= upkr_decode_bit(context_index + 1) << bit_pos++;
-        context_index += 2;
-    }
-    return length | (1 << bit_pos);
-}
-
-void* upkr_unpack(void* destination, void* compressed_data) {
-    upkr_data_ptr = (u8*)compressed_data;
-    upkr_state = 0;
-#ifdef UPKR_BITSTREAM
-    upkr_bits_left = 0;
-#endif
-    for(int i = 0; i < sizeof(upkr_probs); ++i)
-        upkr_probs[i] = 128;
-    
-    u8* write_ptr = (u8*)destination;
-    
-    int prev_was_match = 0;
-    int offset = 0;
-    for(;;) {
-        if(upkr_decode_bit(0)) {
-            if(prev_was_match || upkr_decode_bit(256)) {
-                offset = upkr_decode_length(257) - 1;
-                if(offset == 0) {
-                    break;
-                }
-            }
-            int length = upkr_decode_length(257 + 64);
-            while(length--) {
-                *write_ptr = write_ptr[-offset];
-                ++write_ptr;
-            }
-            prev_was_match = 1;
-        } else {
-            int byte = 1;
-            while(byte < 256) {
-                int bit = upkr_decode_bit(byte);
-                byte = (byte << 1) + bit;
-            }
-            *write_ptr++ = byte;
-            prev_was_match = 0;
-        }
-    }
-    
-    return write_ptr;
-}

asm_unpackers/unpack_armv6m.S

@@ -1,162 +0,0 @@
-// armv6-m upkr unpacker by yrlf
-// some optimizations by exoticorn
-
-.syntax unified
-.thumb
-
-.section .text
-
-#define ALIGNUP(n, align) (((n) + (align) - 1) & ~((align) - 1))
-#define PROB_LEN (1 + 255 + 1 + 2*32 + 2*32)
-#define FRAME_SIZE ALIGNUP(PROB_LEN, 4)
-
-// auto upkr_unpack(uint8_t * out, uint8_t * in) -> tuple<uint8_t *, uint8_t *>
-.global upkr_unpack
-.type upkr_unpack, %function
-// r0 .. out_ptr (returned)
-// r1 .. in_ptr (returned)
-// r2 .. state
-// r3 .. offset
-// r4 .. prev_was_literal / decode_length ret
-// r5 .. subroutine arg (preserved)
-// r6 .. decode_bit ret
-// r7 .. probs ptr
-upkr_unpack:
-    push { r4, r5, r6, r7, lr }
-    sub sp, sp, #FRAME_SIZE
-
-    mov r7, sp
-    movs r2, #255
-    adds r2, r2, #(PROB_LEN - 255)
-    movs r3, #128
-.Lclear:
-    subs r2, r2, #1
-    strb r3, [r7, r2]
-    bne .Lclear
-
-.Lloop:
-    movs r5, #0
-    bl upkr_decode_bit
-    beq .Ldata
-.Lmatch:
-    // r6 = 1
-    lsls r5, r6, #8
-    cmp r4, #0
-    beq 1f
-
-    bl upkr_decode_bit
-    beq 2f
-
-1:
-    bl upkr_decode_length
-    adds r3, r4, #1
-    beq .Lend
-2:
-
-    adds r5, r5, #64
-    bl upkr_decode_length
-.Lcopy_loop:
-    ldrb r5, [r0, r3]
-.Lstore:
-    strb r5, [r0]
-    adds r0, r0, #1
-    adds r4, r4, #1
-    blt .Lcopy_loop
-    b .Lloop
-
-.Ldata:
-    movs r5, #1
-
-.Ldata_loop:
-    bl upkr_decode_bit
-    adcs r5, r5, r5
-    lsrs r4, r5, #8
-    beq .Ldata_loop
-    b .Lstore
-
-.Lend:
-    add sp, sp, #FRAME_SIZE
-    pop { r4, r5, r6, r7, pc }
-
-.type upkr_decode_length, %function
-// r0 .. -length tmp (saved)
-// r1 ..
-// r2 ..
-// r3 ..
-// r4 .. -length (returned)
-// r5 .. context index (saved)
-// r6 .. (saved)
-// r7 ..
-upkr_decode_length:
-    push { r0, r5, r6, lr }
-
-    movs r0, #0
-    subs r4, r0, #1
-.Lbit_loop:
-    adds r5, r5, #1
-    bl upkr_decode_bit
-    beq 1f
-
-    adds r5, r5, #1
-    bl upkr_decode_bit
-    beq 2f
-    adds r0, r0, r4
-2:
-    lsls r4, r4, #1
-    b .Lbit_loop
-1:
-    adds r4, r4, r0
-
-    pop { r0, r5, r6, pc }
-
-.type upkr_decode_bit, %function
-// r0 .. tmp / prob (saved)
-// r1 .. in_ptr (modified)
-// r2 .. state (modified)
-// r3 .. scratch (saved)
-// r4 ..
-// r5 .. context index (preserved)
-// r6 .. bit (returned)
-// r7 .. probs ptr (preserved)
-upkr_fill_state:
-    lsls r2, r2, #8
-    ldrb r6, [r1]
-    adds r1, r1, #1
-    orrs r2, r2, r6
-
-upkr_decode_bit:
-    lsrs r6, r2, #12
-    beq upkr_fill_state
-
-    push { r0, r1, r3, lr }
-
-    ldrb r0, [r7, r5]
-
-    lsrs r3, r2, #8
-    uxtb r1, r2
-
-    subs r6, r1, r0
-    blt 1f
-
-    subs r1, r2, r0
-    rsbs r0, r0, #0
-1:
-
-    muls r3, r3, r0
-    adds r2, r1, r3
-
-    rsbs r3, r0, #0
-    uxtb r3, r3
-    lsrs r3, r3, #4
-    adcs r0, r0, r3
-
-    cmp r6, #0
-    blt 1f
-
-    rsbs r0, r0, #0
-1:
-
-    strb r0, [r7, r5]
-
-    lsrs r6, r6, #31
-    pop { r0, r1, r3, pc }

c_unpacker/decode_bit_alt.c

@@ -1,33 +0,0 @@
-int upkr_decode_bit(int context_index) {
-#ifdef UPKR_BITSTREAM
-    while(upkr_state < 32768) {
-        if(upkr_bits_left == 0) {
-            upkr_current_byte = *upkr_data_ptr++;
-            upkr_bits_left = 8;
-        }
-        upkr_state = (upkr_state << 1) + (upkr_current_byte & 1);
-        upkr_current_byte >>= 1;
-        --upkr_bits_left;
-    }
-#else
-    while(upkr_state < 4096) {
-        upkr_state = (upkr_state << 8) | *upkr_data_ptr++;
-    }
-#endif
-   
-    int prob = upkr_probs[context_index];
-    int bit = (upkr_state & 255) < prob ? 1 : 0;
-    
-    if(bit) {
-        prob = 256 - prob;
-    }
-    upkr_state -= prob * ((upkr_state >> 8) + (bit ^ 1));
-    prob -= (prob + 8) >> 4;
-    if(bit) {
-        prob = -prob;
-    }
-    upkr_probs[context_index] = prob;
-
-    return bit;
-}
-

c_unpacker/main.c

@@ -1,7 +1,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 
-void* upkr_unpack(void* destination, void* compressed_data);
+int upkr_unpack(void* destination, void* compressed_data);
 
 int main(int argn, char** argv) {
   void* input_buffer = malloc(1024*1024);
@@ -13,8 +13,7 @@ int main(int argn, char** argv) {
   
   printf("Compressed size: %d\n", in_size);
   
-  void* end_ptr = upkr_unpack(output_buffer, input_buffer);
+  int out_size = upkr_unpack(output_buffer, input_buffer);
-  int out_size = (char*)end_ptr - (char*)output_buffer;
   
   printf("Uncompressed size: %d\n", out_size);
   

c_unpacker/unpack.c

@@ -19,8 +19,8 @@ int upkr_decode_bit(int context_index) {
             upkr_current_byte = *upkr_data_ptr++;
             upkr_bits_left = 8;
         }
-        upkr_state = (upkr_state << 1) + (upkr_current_byte & 1);
+        upkr_state = (upkr_state << 1) + (upkr_current_byte >> 7);
-        upkr_current_byte >>= 1;
+        upkr_current_byte <<= 1;
         --upkr_bits_left;
     }
 #else
@@ -30,16 +30,18 @@ int upkr_decode_bit(int context_index) {
 #endif
    
     int prob = upkr_probs[context_index];
-    int bit = (upkr_state & 255) < prob ? 1 : 0;
+    int bit = (upkr_state & 255) >= prob ? 1 : 0;
     
+    int prob_offset = 16;
+    int state_offset = 0;
+    int state_scale = prob;
     if(bit) {
-        upkr_state = prob * (upkr_state >> 8) + (upkr_state & 255);
+        state_offset = -prob;
-        prob += (256 - prob + 8) >> 4;
+        state_scale = 256 - prob;
-    } else {
+        prob_offset = 0;
-        upkr_state = (256 - prob) * (upkr_state >> 8) + (upkr_state & 255) - prob;
-        prob -= (prob + 8) >> 4;
     }
-    upkr_probs[context_index] = prob;
+    upkr_state = state_offset + state_scale * (upkr_state >> 8) + (upkr_state & 255);
+    upkr_probs[context_index] = prob_offset + prob - ((prob + 8) >> 4); 
 
     return bit;
 }
@@ -54,7 +56,7 @@ int upkr_decode_length(int context_index) {
     return length | (1 << bit_pos);
 }
 
-void* upkr_unpack(void* destination, void* compressed_data) {
+int upkr_unpack(void* destination, void* compressed_data) {
     upkr_data_ptr = (u8*)compressed_data;
     upkr_state = 0;
 #ifdef UPKR_BITSTREAM
@@ -92,5 +94,5 @@ void* upkr_unpack(void* destination, void* compressed_data) {
         }
     }
     
-    return write_ptr;
+    return write_ptr - (u8*)destination;
 }

src/context_state.rs

@@ -1,8 +1,8 @@
-use crate::rans::{PROB_BITS, ONE_PROB};
+use crate::rans::{ONE_PROB, PROB_BITS};
 
 const INIT_PROB: u16 = 1 << (PROB_BITS - 1);
-const UPDATE_RATE: u32 = 4;
+const UPDATE_RATE: i32 = 4;
-const UPDATE_ADD: u32 = 8;
+const UPDATE_ADD: i32 = 8;
 
 #[derive(Clone)]
 pub struct ContextState {
@@ -33,10 +33,13 @@ impl<'a> Context<'a> {
 
     pub fn update(&mut self, bit: bool) {
         let old = self.state.contexts[self.index];
-        self.state.contexts[self.index] = if bit {
+        let offset = if !bit {
-            old + ((ONE_PROB - old as u32 + UPDATE_ADD) >> UPDATE_RATE) as u8
+            ONE_PROB as i32 >> UPDATE_RATE
         } else {
-            old - ((old as u32 + UPDATE_ADD) >> UPDATE_RATE) as u8
+            0
         };
+
+        self.state.contexts[self.index] =
+            (offset + old as i32 - ((old as i32 + UPDATE_ADD) >> UPDATE_RATE)) as u8;
     }
 }

src/greedy_packer.rs

@@ -6,12 +6,11 @@ use crate::ProgressCallback;
 pub fn pack(
     data: &[u8],
     use_bitstream: bool,
-    parity_contexts: usize,
     mut progress_callback: Option<ProgressCallback>,
 ) -> Vec<u8> {
     let mut match_finder = MatchFinder::new(data);
     let mut rans_coder = RansCoder::new(use_bitstream);
-    let mut state = lz::CoderState::new(parity_contexts);
+    let mut state = lz::CoderState::new();
 
     let mut pos = 0;
     while pos < data.len() {

src/lib.rs

@@ -13,19 +13,12 @@ pub fn pack(
     data: &[u8],
     level: u8,
     use_bitstream: bool,
-    parity_contexts: usize,
     progress_callback: Option<ProgressCallback>,
 ) -> Vec<u8> {
     if level == 0 {
-        greedy_packer::pack(data, use_bitstream, parity_contexts, progress_callback)
+        greedy_packer::pack(data, use_bitstream, progress_callback)
     } else {
-        parsing_packer::pack(
+        parsing_packer::pack(data, level, use_bitstream, progress_callback)
-            data,
-            level,
-            use_bitstream,
-            parity_contexts,
-            progress_callback,
-        )
     }
 }
 

src/lz.rs

@@ -9,49 +9,41 @@ 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, literal_base, false);
+                encode_bit(coder, state, 0, false);
                 let mut context_index = 1;
                 for i in (0..8).rev() {
                     let bit = (lit >> i) & 1 != 0;
-                    encode_bit(coder, state, literal_base + context_index, bit);
+                    encode_bit(coder, state, 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, literal_base, true);
+                encode_bit(coder, state, 0, true);
                 if !state.prev_was_match {
-                    encode_bit(
+                    encode_bit(coder, state, 256, offset != state.last_offset);
-                        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, 256 * state.parity_contexts + 1, offset + 1);
+                    encode_length(coder, state, 257, offset + 1);
                     state.last_offset = offset;
                 }
-                encode_length(coder, state, 256 * state.parity_contexts + 65, len);
+                encode_length(coder, state, 257 + 64, 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, state.pos % state.parity_contexts * 256, true);
+    encode_bit(coder, state, 0, true);
     if !state.prev_was_match {
-        encode_bit(coder, state, 256 * state.parity_contexts, true);
+        encode_bit(coder, state, 256, true);
     }
-    encode_length(coder, state, 256 * state.parity_contexts + 1, 1);
+    encode_length(coder, state, 257, 1);
 }
 
 fn encode_bit(
@@ -84,20 +76,16 @@ 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(parity_contexts: usize) -> CoderState {
+    pub fn new() -> CoderState {
         CoderState {
-            contexts: ContextState::new((1 + 255) * parity_contexts + 1 + 64 + 64),
+            contexts: ContextState::new(1 + 255 + 1 + 64 + 64),
             last_offset: 0,
-            parity_contexts,
             prev_was_match: false,
-            pos: 0,
         }
     }
 
@@ -106,9 +94,9 @@ impl CoderState {
     }
 }
 
-pub fn unpack(packed_data: &[u8], use_bitstream: bool, parity_contexts: usize) -> Vec<u8> {
+pub fn unpack(packed_data: &[u8], use_bitstream: bool) -> Vec<u8> {
     let mut decoder = RansDecoder::new(packed_data, use_bitstream);
-    let mut contexts = ContextState::new((1 + 255) * parity_contexts + 1 + 64 + 64);
+    let mut contexts = ContextState::new(1 + 255 + 1 + 64 + 64);
     let mut result = vec![];
     let mut offset = 0;
     let mut prev_was_match = false;
@@ -131,17 +119,14 @@ pub fn unpack(packed_data: &[u8], use_bitstream: bool, parity_contexts: usize) -
     }
 
     loop {
-        let literal_base = result.len() % parity_contexts * 256;
+        if decoder.decode_with_context(&mut contexts.context_mut(0)) {
-        if decoder.decode_with_context(&mut contexts.context_mut(literal_base)) {
+            if prev_was_match || decoder.decode_with_context(&mut contexts.context_mut(256)) {
-            if prev_was_match
+                offset = decode_length(&mut decoder, &mut contexts, 257) - 1;
-                || 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, 256 * parity_contexts + 65);
+            let length = decode_length(&mut decoder, &mut contexts, 257 + 64);
             for _ in 0..length {
                 result.push(result[result.len() - offset]);
             }
@@ -150,8 +135,7 @@ pub fn unpack(packed_data: &[u8], use_bitstream: bool, parity_contexts: usize) -
             let mut context_index = 1;
             let mut byte = 0;
             for i in (0..8).rev() {
-                let bit = decoder
+                let bit = decoder.decode_with_context(&mut contexts.context_mut(context_index));
-                    .decode_with_context(&mut contexts.context_mut(literal_base + context_index));
                 context_index = (context_index << 1) | bit as usize;
                 byte |= (bit as u8) << i;
             }

src/main.rs

@@ -1,6 +1,5 @@
 use anyhow::{bail, Result};
 use std::io::prelude::*;
-use std::process;
 use std::{fs::File, path::PathBuf};
 
 fn main() -> Result<()> {
@@ -11,14 +10,6 @@ fn main() -> Result<()> {
         Some("pack") => {
             let level = args.opt_value_from_str(["-l", "--level"])?.unwrap_or(2u8);
             let use_bitstream = args.contains(["-b", "--bitstream"]);
-            let parity_contexts = args
-                .opt_value_from_str(["-p", "--parity"])?
-                .unwrap_or(1usize);
-
-            if parity_contexts != 1 && parity_contexts != 2 && parity_contexts != 4 {
-                eprintln!("--parity has to be 1, 2 or 4");
-                process::exit(1);
-            }
 
             let infile = args.free_from_os_str::<PathBuf, bool>(|s| Ok(s.into()))?;
             let outfile = args.free_from_os_str::<PathBuf, bool>(|s| Ok(s.into()))?;
@@ -32,7 +23,6 @@ fn main() -> Result<()> {
                 &data,
                 level,
                 use_bitstream,
-                parity_contexts,
                 Some(&mut |pos| {
                     pb.set(pos as u64);
                 }),
@@ -49,21 +39,13 @@ fn main() -> Result<()> {
         }
         Some("unpack") => {
             let use_bitstream = args.contains(["-b", "--bitstream"]);
-            let parity_contexts = args
-                .opt_value_from_str(["-p", "--parity"])?
-                .unwrap_or(1usize);
-
-            if parity_contexts != 1 && parity_contexts != 2 && parity_contexts != 4 {
-                eprintln!("--parity has to be 1, 2 or 4");
-                process::exit(1);
-            }
 
             let infile = args.free_from_os_str::<PathBuf, bool>(|s| Ok(s.into()))?;
             let outfile = args.free_from_os_str::<PathBuf, bool>(|s| Ok(s.into()))?;
 
             let mut data = vec![];
             File::open(infile)?.read_to_end(&mut data)?;
-            let packed_data = upkr::unpack(&data, use_bitstream, parity_contexts);
+            let packed_data = upkr::unpack(&data, use_bitstream);
             File::create(outfile)?.write_all(&packed_data)?;
         }
         Some(other) => {
@@ -76,11 +58,10 @@ fn main() -> Result<()> {
 
 fn print_help() {
     eprintln!("Usage:");
-    eprintln!("  upkr pack [-b] [-l level(0-9)] [-p N] <infile> <outfile>");
+    eprintln!("  upkr pack [-b] [-l level(0-9)] <infile> <outfile>");
-    eprintln!("  upkr unpack [-b] [-p N] <infile> <outfile>");
+    eprintln!("  upkr unpack [-b] <infile> <outfile>");
     eprintln!();
     eprintln!(" -b, --bitstream     bitstream mode");
     eprintln!(" -l, --level N       compression level 0-9");
-    eprintln!(" -p, --parity N      use N (2/4) parity contexts");
+    std::process::exit(1);
-    process::exit(1);
 }

src/parsing_packer.rs

@@ -6,25 +6,14 @@ use crate::match_finder::MatchFinder;
 use crate::rans::{CostCounter, RansCoder};
 use crate::{lz, ProgressCallback};
 
-pub fn pack(
+pub fn pack(data: &[u8], level: u8, use_bitstream: bool, progress_cb: Option<ProgressCallback>) -> Vec<u8> {
-    data: &[u8],
+    let mut parse = parse(data, Config::from_level(level), progress_cb);
-    level: u8,
-    use_bitstream: bool,
-    parity_contexts: usize,
-    progress_cb: Option<ProgressCallback>,
-) -> Vec<u8> {
-    let mut parse = parse(
-        data,
-        Config::from_level(level),
-        parity_contexts,
-        progress_cb,
-    );
     let mut ops = vec![];
     while let Some(link) = parse {
         ops.push(link.op);
         parse = link.prev.clone();
     }
-    let mut state = lz::CoderState::new(parity_contexts);
+    let mut state = lz::CoderState::new();
     let mut coder = RansCoder::new(use_bitstream);
     for op in ops.into_iter().rev() {
         op.encode(&mut coder, &mut state);
@@ -49,7 +38,6 @@ type Arrivals = HashMap<usize, Vec<Arrival>>;
 fn parse(
     data: &[u8],
     config: Config,
-    parity_contexts: usize,
     mut progress_cb: Option<ProgressCallback>,
 ) -> Option<Rc<Parse>> {
     let mut match_finder = MatchFinder::new(data)
@@ -141,7 +129,7 @@ fn parse(
         0,
         Arrival {
             parse: None,
-            state: lz::CoderState::new(parity_contexts),
+            state: lz::CoderState::new(),
             cost: 0.0,
         },
         max_arrivals,

src/rans.rs

@@ -38,15 +38,15 @@ impl RansCoder {
         let mut state = 1 << l_bits;
 
         let mut byte = 0u8;
-        let mut bit = 8;
+        let mut bit = 0;
         let mut flush_state: Box<dyn FnMut(&mut u32)> = if self.use_bitstream {
             Box::new(|state: &mut u32| {
-                bit -= 1;
                 byte |= ((*state & 1) as u8) << bit;
-                if bit == 0 {
+                bit += 1;
+                if bit == 8 {
                     buffer.push(byte);
                     byte = 0;
-                    bit = 8;
+                    bit = 0;
                 }
                 *state >>= 1;
             })
@@ -61,7 +61,7 @@ impl RansCoder {
         let max_state_factor: u32 = 1 << (l_bits + num_flush_bits - PROB_BITS);
         for step in self.bits.into_iter().rev() {
             let prob = step as u32 & 32767;
-            let (start, prob) = if step & 32768 != 0 {
+            let (start, prob) = if step & 32768 == 0 {
                 (0, prob)
             } else {
                 (prob, ONE_PROB - prob)
@@ -118,7 +118,7 @@ impl CostCounter {
 
 impl EntropyCoder for CostCounter {
     fn encode_bit(&mut self, bit: bool, prob: u16) {
-        let prob = if bit {
+        let prob = if !bit {
             prob as u32
         } else {
             ONE_PROB - prob as u32
@@ -163,8 +163,8 @@ impl<'a> RansDecoder<'a> {
                     self.data = &self.data[1..];
                     self.bits_left = 8;
                 }
-                self.state = (self.state << 1) | (self.byte & 1) as u32;
+                self.state = (self.state << 1) | (self.byte >> 7) as u32;
-                self.byte >>= 1;
+                self.byte <<= 1;
                 self.bits_left -= 1;
             }
         } else {
@@ -174,12 +174,12 @@ impl<'a> RansDecoder<'a> {
             }
         }
 
-        let bit = (self.state & PROB_MASK) < prob;
+        let bit = (self.state & PROB_MASK) >= prob;
 
         let (start, prob) = if bit {
-            (0, prob)
-        } else {
             (prob, ONE_PROB - prob)
+        } else {
+            (0, prob)
         };
         self.state = prob * (self.state >> PROB_BITS) + (self.state & PROB_MASK) - start;