Merge branch 'ped7g-z80_ped7g'

missing 512 byte table generator, which doesn't look trivial to do
(especially in terms of code size).
Not tested, but looks as decent speed up.

Cargo.lock

@@ -62,6 +62,12 @@ version = "1.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
 
+[[package]]
+name = "lexopt"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "478ee9e62aaeaf5b140bd4138753d1f109765488581444218d3ddda43234f3e8"
+
 [[package]]
 name = "libc"
 version = "0.2.108"
@@ -90,10 +96,22 @@ dependencies = [
 ]
 
 [[package]]
-name = "pico-args"
+name = "proc-macro2"
-version = "0.4.2"
+version = "1.0.44"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "db8bcd96cb740d03149cbad5518db9fd87126a10ab519c011893b1754134c468"
+checksum = "7bd7356a8122b6c4a24a82b278680c73357984ca2fc79a0f9fa6dea7dced7c58"
+dependencies = [
+ "unicode-ident",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bbe448f377a7d6961e30f5955f9b8d106c3f5e449d493ee1b125c1d43c2b5179"
+dependencies = [
+ "proc-macro2",
+]
 
 [[package]]
 name = "sacabase"
@@ -104,6 +122,37 @@ dependencies = [
  "num-traits",
 ]
 
+[[package]]
+name = "syn"
+version = "1.0.101"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e90cde112c4b9690b8cbe810cba9ddd8bc1d7472e2cae317b69e9438c1cba7d2"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
+[[package]]
+name = "thiserror"
+version = "1.0.36"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0a99cb8c4b9a8ef0e7907cd3b617cc8dc04d571c4e73c8ae403d80ac160bb122"
+dependencies = [
+ "thiserror-impl",
+]
+
+[[package]]
+name = "thiserror-impl"
+version = "1.0.36"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3a891860d3c8d66fec8e73ddb3765f90082374dbaaa833407b904a94f1a7eb43"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "time"
 version = "0.1.44"
@@ -115,14 +164,21 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "unicode-ident"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dcc811dc4066ac62f84f11307873c4850cb653bfa9b1719cee2bd2204a4bc5dd"
+
 [[package]]
 name = "upkr"
-version = "0.1.0"
+version = "0.2.0-pre3"
 dependencies = [
  "anyhow",
  "cdivsufsort",
+ "lexopt",
  "pbr",
- "pico-args",
+ "thiserror",
 ]
 
 [[package]]

Cargo.toml

@@ -1,12 +1,13 @@
 [package]
 name = "upkr"
-version = "0.1.0"
+version = "0.2.0-pre3"
 edition = "2021"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
 cdivsufsort = "2"
-pico-args = "0.4"
+lexopt = "0.2.1"
 anyhow = "1"
+thiserror = "1.0.36"
 pbr = "1"

asm_unpackers/.gitignore

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

asm_unpackers/Makefile

@@ -0,0 +1,51 @@
+build/unpack_riscv64: ../c_unpacker/main.c unpack_riscv.S
+	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_riscv64.o: unpack_riscv.S
+	mkdir -p build
+	riscv64-linux-gnu-gcc -c -o $@ $?
+
+build/unpack_riscv64.bin: build/unpack_riscv64.o
+	riscv64-linux-gnu-objcopy -O binary --only-section=.text $? $@
+
+disas-riscv64: build/unpack_riscv64.o
+	riscv64-linux-gnu-objdump -d $?
+
+build/unpack_riscv32.o: unpack_riscv.S
+	mkdir -p build
+	riscv64-linux-gnu-gcc -march=rv32imc -mabi=ilp32 -c -o $@ $?
+	
+build/unpack_riscv32.bin: build/unpack_riscv32.o
+	riscv64-linux-gnu-objcopy -O binary --only-section=.text $? $@
+
+disas-riscv32: build/unpack_riscv32.o
+	riscv64-linux-gnu-objdump -d $?
+
+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
+	mkdir -p build
+	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 build/unpack_riscv64.bin build/unpack_riscv32.bin
+	ls -l build/*.bin

asm_unpackers/test_data.bin

@@ -0,0 +1,99 @@
+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

@@ -0,0 +1,162 @@
+// 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 }

asm_unpackers/unpack_riscv.S

@@ -0,0 +1,142 @@
+.section .text
+
+#define FRAME_SIZE (256+32*4+4)
+
+// x8 prob array ptr
+// x9 prev was literal
+// x10 out ptr
+// x11 in ptr
+// x12 offset
+// x13 state
+
+.global upkr_unpack
+.type upkr_unpack, %function
+upkr_unpack:
+	mv t4, ra
+	mv x17, x8
+	mv t6, x9
+	li x13, FRAME_SIZE
+	li x9, 128
+1:
+	addi sp, sp, -1
+	sb x9, 0(sp)
+	addi x13, x13, -1
+	bnez x13, 1b
+	
+.Lmainloop:
+	li x14, 0
+	jal upkr_decode_bit
+	beqz x15, .Lliteral
+	
+	slli x14, x14, 8
+	beqz x9, .Lread_offset_inc_x14
+	jal upkr_decode_bit
+	bnez x15, .Lread_offset
+
+.Lfinished_offset:
+	addi x14, x14, 64
+	jal t3, upkr_decode_number
+1:
+	add x14, x10, t0
+	lbu x14, (x14)
+.Lstore_byte:
+	sb x14, (x10)
+	addi x10, x10, 1
+	addi x9, x9, 1
+	blt x9, x0, 1b
+	j .Lmainloop
+	
+.Lliteral:
+	jal upkr_decode_bit
+	addi x14, x14, -1
+	slli x14, x14, 1
+	add x14, x14, x15
+	srli x9, x14, 8
+	beqz x9, .Lliteral
+	j .Lstore_byte
+
+.Lread_offset_inc_x14:
+	addi x14, x14, 1
+.Lread_offset:
+	jal t3, upkr_decode_number
+	addi t0, x9, 1
+	bnez t0, .Lfinished_offset
+.Ldone:
+	addi sp, sp, FRAME_SIZE
+	mv x8, x17
+	mv x9, t6
+	jr t4
+
+// x14 context index
+// return: x9 negtive decoded number 
+upkr_decode_number:
+	mv t5, x14
+	li x9, 0
+	li x8, -1
+1:
+	jal upkr_decode_bit
+	beqz x15, 1f
+	jal upkr_decode_bit
+	beqz x15, 2f
+	add x9, x9, x8
+2:
+	slli x8, x8, 1
+	j 1b
+1:
+	add x9, x9, x8
+	
+	mv x14, t5
+	jr t3
+
+upkr_load_byte:
+	lbu x15, 0(x11)
+	addi x11, x11, 1
+	slli x13, x13, 8
+	add x13, x13, x15
+// x8 prob array ptr
+// x11 in ptr
+// x13 state
+// x14 context index
+// return:
+//   x14 context index + 1
+//   x15 decoded bit
+upkr_decode_bit:
+	srli x15, x13, 12
+	beqz x15, upkr_load_byte
+
+	mv t1, x14
+	mv t2, x10
+	
+	add x14, x14, sp
+	lbu x12, 0(x14)
+	
+	andi x10, x13, 255
+	sltu x15, x10, x12
+	srli x13, x13, 8
+	beqz x15, .Lelse
+	
+	mul x13, x13, x12
+	add x13, x13, x10
+	li x10, 256 + 8
+	sub x10, x10, x12
+	srli x10, x10, 4
+	add x12, x12, x10
+	j .Lendif
+
+.Lelse:
+	li x16, 256
+	sub x16, x16, x12
+	mul x13, x13, x16
+	add x13, x13, x10
+	sub x13, x13, x12
+	addi x10, x12, 8
+	srli x10, x10, 4
+	sub x12, x12, x10
+
+.Lendif:
+
+	sb x12, 0(x14)
+	
+	addi x14, t1, 1
+	mv x10, t2
+	ret

c_unpacker/decode_bit_alt.c

@@ -0,0 +1,33 @@
+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>
 
-int upkr_unpack(void* destination, void* compressed_data);
+void* upkr_unpack(void* destination, void* compressed_data);
 
 int main(int argn, char** argv) {
   void* input_buffer = malloc(1024*1024);
@@ -13,7 +13,8 @@ int main(int argn, char** argv) {
   
   printf("Compressed size: %d\n", in_size);
   
-  int out_size = upkr_unpack(output_buffer, input_buffer);
+  void* end_ptr = 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 >> 7);
+        upkr_state = (upkr_state << 1) + (upkr_current_byte & 1);
-        upkr_current_byte <<= 1;
+        upkr_current_byte >>= 1;
         --upkr_bits_left;
     }
 #else
@@ -30,18 +30,16 @@ 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) {
-        state_offset = -prob;
+        upkr_state = prob * (upkr_state >> 8) + (upkr_state & 255);
-        state_scale = 256 - prob;
+        prob += (256 - prob + 8) >> 4;
-        prob_offset = 0;
+    } else {
+        upkr_state = (256 - prob) * (upkr_state >> 8) + (upkr_state & 255) - prob;
+        prob -= (prob + 8) >> 4;
     }
-    upkr_state = state_offset + state_scale * (upkr_state >> 8) + (upkr_state & 255);
+    upkr_probs[context_index] = prob;
-    upkr_probs[context_index] = prob_offset + prob - ((prob + 8) >> 4); 
 
     return bit;
 }
@@ -56,7 +54,7 @@ int upkr_decode_length(int context_index) {
     return length | (1 << bit_pos);
 }
 
-int upkr_unpack(void* destination, void* compressed_data) {
+void* upkr_unpack(void* destination, void* compressed_data) {
     upkr_data_ptr = (u8*)compressed_data;
     upkr_state = 0;
 #ifdef UPKR_BITSTREAM
@@ -94,5 +92,5 @@ int upkr_unpack(void* destination, void* compressed_data) {
         }
     }
     
-    return write_ptr - (u8*)destination;
+    return write_ptr;
 }

compare-variants

@@ -1,50 +0,0 @@
-#!/bin/env ruby
-
-configs = [
-    [:master, '-b'],
-    [:z80, '-b'],
-    [:z80, ['-b', '-r']],
-    ['old-prob-update', '-b']
-]
-
-files = Dir[ARGV[0] + '/*'].select {|f| !(f =~ /\.txt$/) }
-short_names = files.map {|f| File.basename(f)[..16] }
-results = []
-
-def print_results(configs, names, results)
-    configs.each_with_index do |config, i|
-        printf "%d: %s\n", i + 1, config
-    end
-    
-    print '                '
-    configs.each_index do |i|
-        printf "  %-4d", i + 1
-    end
-    puts
-    names.each_with_index do |name, i|
-        printf "%16s", name
-        for res in results
-            res = res[i]
-            printf "  %-4s", res if res
-        end
-        puts
-    end
-end
-
-for config in configs
-    raise unless system('git', 'checkout', config[0].to_s)
-    config_results = []
-    results << config_results
-    for file in files
-        if system(*['cargo', 'run', '--release', 'pack', '-l', '9', config[1], file, '/tmp/out.upk'].flatten) &&
-            system(*['cargo', 'run', '--release', 'unpack', config[1], '/tmp/out.upk', '/tmp/out.bin'].flatten) &&
-            File.read(file) == File.read('/tmp/out.bin')
-            size = File.size('/tmp/out.upk')
-            config_results << size
-        else
-            config_results << 'ERR'
-        end
-        print_results(configs, short_names, results)
-    end
-end
-

fuzz/.gitignore

@@ -0,0 +1,3 @@
+target
+corpus
+artifacts

fuzz/Cargo.lock

@@ -0,0 +1,247 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
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+
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+
+[[package]]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
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+
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+ "jobserver",
+]
+
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+ "cc",
+ "sacabase",
+]
+
+[[package]]
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+
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+ "cfg-if",
+ "crossbeam-utils",
+]
+
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+ "cfg-if",
+ "once_cell",
+]
+
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+ "libc",
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+
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+
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+dependencies = [
+ "arbitrary",
+ "cc",
+ "once_cell",
+]
+
+[[package]]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "578ede34cf02f8924ab9447f50c28075b4d3e5b269972345e7e0372b38c6cdcd"
+dependencies = [
+ "autocfg",
+]
+
+[[package]]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
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+
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+ "crossbeam-channel",
+ "libc",
+ "time",
+ "winapi",
+]
+
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+ "unicode-ident",
+]
+
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+ "proc-macro2",
+]
+
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+ "num-traits",
+]
+
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+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
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+ "thiserror-impl",
+]
+
+[[package]]
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+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
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+checksum = "6db9e6914ab8b1ae1c260a4ae7a49b6c5611b40328a735b21862567685e73255"
+dependencies = [
+ "libc",
+ "wasi",
+ "winapi",
+]
+
+[[package]]
+name = "unicode-ident"
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+
+[[package]]
+name = "upkr"
+version = "0.2.0-pre3"
+dependencies = [
+ "anyhow",
+ "cdivsufsort",
+ "lexopt",
+ "pbr",
+ "thiserror",
+]
+
+[[package]]
+name = "upkr-fuzz"
+version = "0.0.0"
+dependencies = [
+ "libfuzzer-sys",
+ "upkr",
+]
+
+[[package]]
+name = "wasi"
+version = "0.10.0+wasi-snapshot-preview1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1a143597ca7c7793eff794def352d41792a93c481eb1042423ff7ff72ba2c31f"
+
+[[package]]
+name = "winapi"
+version = "0.3.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5c839a674fcd7a98952e593242ea400abe93992746761e38641405d28b00f419"
+dependencies = [
+ "winapi-i686-pc-windows-gnu",
+ "winapi-x86_64-pc-windows-gnu",
+]
+
+[[package]]
+name = "winapi-i686-pc-windows-gnu"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ac3b87c63620426dd9b991e5ce0329eff545bccbbb34f3be09ff6fb6ab51b7b6"
+
+[[package]]
+name = "winapi-x86_64-pc-windows-gnu"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"

fuzz/Cargo.toml

@@ -0,0 +1,31 @@
+[package]
+name = "upkr-fuzz"
+version = "0.0.0"
+authors = ["Automatically generated"]
+publish = false
+edition = "2018"
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+libfuzzer-sys = "0.4"
+
+[dependencies.upkr]
+path = ".."
+
+# Prevent this from interfering with workspaces
+[workspace]
+members = ["."]
+
+[[bin]]
+name = "all_configs"
+path = "fuzz_targets/all_configs.rs"
+test = false
+doc = false
+
+[[bin]]
+name = "unpack"
+path = "fuzz_targets/unpack.rs"
+test = false
+doc = false

fuzz/fuzz_targets/all_configs.rs

@@ -0,0 +1,29 @@
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+
+fuzz_target!(|data: &[u8]| {
+    let mut config = upkr::Config::default();
+    let mut level = 1;
+    let mut data = data;
+    if data.len() > 2 {
+        let flags1 = data[0];
+        let flags2 = data[1];
+        data = &data[2..];
+        config.use_bitstream = (flags1 & 1) != 0;
+        config.parity_contexts = if (flags1 & 2) == 0 { 1 } else { 2 };
+        config.invert_bit_encoding = (flags1 & 4) != 0;
+        config.is_match_bit = (flags1 & 8) != 0;
+        config.new_offset_bit = (flags1 & 16) != 0;
+        config.continue_value_bit = (flags1 & 32) != 0;
+        config.bitstream_is_big_endian = (flags1 & 64) != 0;
+        config.simplified_prob_update = (flags1 & 128) != 0;
+        config.no_repeated_offsets = (flags2 & 32) != 0;
+        config.eof_in_length = (flags2 & 1) != 0;
+        config.max_offset = if (flags2 & 2) == 0 { usize::MAX } else { 32 };
+        config.max_length = if (flags2 & 4) == 0 { usize::MAX } else { 5 };
+        level = (flags2 >> 3) & 3;
+    }
+    let packed = upkr::pack(data, level, &config, None);
+    let unpacked = upkr::unpack(&packed, &config, 1024 * 1024).unwrap();
+    assert!(unpacked == data);
+});

fuzz/fuzz_targets/unpack.rs

@@ -0,0 +1,6 @@
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+
+fuzz_target!(|data: &[u8]| {
+    let _ = upkr::unpack(data, &upkr::Config::default(), 64 * 1024);
+});

src/context_state.rs

@@ -1,12 +1,17 @@
-use crate::rans::{ONE_PROB, PROB_BITS};
+use crate::{
+    rans::{ONE_PROB, PROB_BITS},
+    Config,
+};
 
 const INIT_PROB: u16 = 1 << (PROB_BITS - 1);
-const UPDATE_RATE: i32 = 4;
+const UPDATE_RATE: u32 = 4;
-const UPDATE_ADD: i32 = 8;
+const UPDATE_ADD: u32 = 8;
 
 #[derive(Clone)]
 pub struct ContextState {
     contexts: Vec<u8>,
+    invert_bit_encoding: bool,
+    simplified_prob_update: bool,
 }
 
 pub struct Context<'a> {
@@ -15,9 +20,11 @@ pub struct Context<'a> {
 }
 
 impl ContextState {
-    pub fn new(size: usize) -> ContextState {
+    pub fn new(size: usize, config: &Config) -> ContextState {
         ContextState {
             contexts: vec![INIT_PROB as u8; size],
+            invert_bit_encoding: config.invert_bit_encoding,
+            simplified_prob_update: config.simplified_prob_update,
         }
     }
 
@@ -33,12 +40,21 @@ impl<'a> Context<'a> {
 
     pub fn update(&mut self, bit: bool) {
         let old = self.state.contexts[self.index];
-        if bit {
+
-            self.state.contexts[self.index] =
+        self.state.contexts[self.index] = if self.state.simplified_prob_update {
-                old - ((old as i32 + UPDATE_ADD) >> UPDATE_RATE) as u8;
+            let offset = if bit ^ self.state.invert_bit_encoding {
+                ONE_PROB as i32 >> UPDATE_RATE
+            } else {
+                0
+            };
+
+            (offset + old as i32 - ((old as i32 + UPDATE_ADD as i32) >> UPDATE_RATE)) as u8
         } else {
-            self.state.contexts[self.index] =
+            if bit ^ self.state.invert_bit_encoding {
-                old + (((ONE_PROB as i32 - old as i32) + UPDATE_ADD) >> UPDATE_RATE) as u8;
+                old + ((ONE_PROB - old as u32 + UPDATE_ADD) >> UPDATE_RATE) as u8
-        }
+            } else {
+                old - ((old as u32 + UPDATE_ADD) >> UPDATE_RATE) as u8
+            }
+        };
     }
 }

src/greedy_packer.rs

@@ -1,16 +1,16 @@
-use crate::lz;
 use crate::match_finder::MatchFinder;
 use crate::rans::RansCoder;
 use crate::ProgressCallback;
+use crate::{lz, Config};
 
 pub fn pack(
     data: &[u8],
-    use_bitstream: bool,
+    config: &Config,
     mut progress_callback: Option<ProgressCallback>,
 ) -> Vec<u8> {
     let mut match_finder = MatchFinder::new(data);
-    let mut rans_coder = RansCoder::new(use_bitstream);
+    let mut rans_coder = RansCoder::new(config);
-    let mut state = lz::CoderState::new();
+    let mut state = lz::CoderState::new(config);
 
     let mut pos = 0;
     while pos < data.len() {
@@ -19,15 +19,16 @@ pub fn pack(
         }
         let mut encoded_match = false;
         if let Some(m) = match_finder.matches(pos).next() {
-            let max_offset = 1 << (m.length * 3 - 1).min(31);
+            let max_offset = config.max_offset.min(1 << (m.length * 3 - 1).min(31));
             let offset = pos - m.pos;
-            if offset < max_offset {
+            if offset < max_offset && m.length >= config.min_length() {
+                let length = m.length.min(config.max_length);
                 lz::Op::Match {
                     offset: offset as u32,
-                    len: m.length as u32,
+                    len: length as u32,
                 }
-                .encode(&mut rans_coder, &mut state);
+                .encode(&mut rans_coder, &mut state, config);
-                pos += m.length;
+                pos += length;
                 encoded_match = true;
             }
         }
@@ -39,13 +40,14 @@ pub fn pack(
                     .iter()
                     .zip(data[(pos - offset)..].iter())
                     .take_while(|(a, b)| a == b)
-                    .count();
+                    .count()
-                if length > 0 {
+                    .min(config.max_length);
+                if length >= config.min_length() {
                     lz::Op::Match {
                         offset: offset as u32,
                         len: length as u32,
                     }
-                    .encode(&mut rans_coder, &mut state);
+                    .encode(&mut rans_coder, &mut state, config);
                     pos += length;
                     encoded_match = true;
                 }
@@ -53,11 +55,11 @@ pub fn pack(
         }
 
         if !encoded_match {
-            lz::Op::Literal(data[pos]).encode(&mut rans_coder, &mut state);
+            lz::Op::Literal(data[pos]).encode(&mut rans_coder, &mut state, config);
             pos += 1;
         }
     }
 
-    lz::encode_eof(&mut rans_coder, &mut state);
+    lz::encode_eof(&mut rans_coder, &mut state, config);
     rans_coder.finish()
 }

src/lib.rs

@@ -5,20 +5,73 @@ mod match_finder;
 mod parsing_packer;
 mod rans;
 
-pub use lz::unpack;
+pub use lz::{calculate_margin, unpack, UnpackError};
 
 pub type ProgressCallback<'a> = &'a mut dyn FnMut(usize);
 
+#[derive(Debug)]
+pub struct Config {
+    pub use_bitstream: bool,
+    pub parity_contexts: usize,
+
+    pub invert_bit_encoding: bool,
+    pub is_match_bit: bool,
+    pub new_offset_bit: bool,
+    pub continue_value_bit: bool,
+
+    pub bitstream_is_big_endian: bool,
+    pub simplified_prob_update: bool,
+
+    pub no_repeated_offsets: bool,
+    pub eof_in_length: bool,
+
+    pub max_offset: usize,
+    pub max_length: usize,
+}
+
+impl Default for Config {
+    fn default() -> Config {
+        Config {
+            use_bitstream: false,
+            parity_contexts: 1,
+
+            invert_bit_encoding: false,
+            is_match_bit: true,
+            new_offset_bit: true,
+            continue_value_bit: true,
+
+            bitstream_is_big_endian: false,
+            simplified_prob_update: false,
+
+            no_repeated_offsets: false,
+            eof_in_length: false,
+
+            max_offset: usize::MAX,
+            max_length: usize::MAX,
+        }
+    }
+}
+
+impl Config {
+    pub fn min_length(&self) -> usize {
+        if self.eof_in_length {
+            2
+        } else {
+            1
+        }
+    }
+}
+
 pub fn pack(
     data: &[u8],
     level: u8,
-    use_bitstream: bool,
+    config: &Config,
     progress_callback: Option<ProgressCallback>,
 ) -> Vec<u8> {
     if level == 0 {
-        greedy_packer::pack(data, use_bitstream, progress_callback)
+        greedy_packer::pack(data, config, progress_callback)
     } else {
-        parsing_packer::pack(data, level, use_bitstream, progress_callback)
+        parsing_packer::pack(data, level, config, progress_callback)
     }
 }
 

src/lz.rs

@@ -1,5 +1,7 @@
 use crate::context_state::ContextState;
 use crate::rans::{EntropyCoder, RansDecoder};
+use crate::Config;
+use thiserror::Error;
 
 #[derive(Copy, Clone, Debug)]
 pub enum Op {
@@ -8,42 +10,73 @@ pub enum Op {
 }
 
 impl Op {
-    pub fn encode(&self, coder: &mut dyn EntropyCoder, state: &mut CoderState) {
+    pub fn encode(&self, coder: &mut dyn EntropyCoder, state: &mut CoderState, config: &Config) {
+        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, !config.is_match_bit);
                 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, config.is_match_bit);
-                if !state.prev_was_match {
+                let mut new_offset = true;
-                    encode_bit(coder, state, 256, offset != state.last_offset);
+                if !state.prev_was_match && !config.no_repeated_offsets {
-                } else {
+                    new_offset = offset != state.last_offset;
-                    assert!(offset != state.last_offset);
+                    encode_bit(
+                        coder,
+                        state,
+                        256 * state.parity_contexts,
+                        new_offset == config.new_offset_bit,
+                    );
                 }
-                if offset != state.last_offset {
+                assert!(offset as usize <= config.max_offset);
-                    encode_length(coder, state, 257, offset + 1);
+                if new_offset {
+                    encode_length(
+                        coder,
+                        state,
+                        256 * state.parity_contexts + 1,
+                        offset + if config.eof_in_length { 0 } else { 1 },
+                        config,
+                    );
                     state.last_offset = offset;
                 }
-                encode_length(coder, state, 257 + 64, len);
+                assert!(len as usize >= config.min_length() && len as usize <= config.max_length);
+                encode_length(coder, state, 256 * state.parity_contexts + 65, len, config);
                 state.prev_was_match = true;
+                state.pos += len as usize;
             }
         }
     }
 }
 
-pub fn encode_eof(coder: &mut dyn EntropyCoder, state: &mut CoderState) {
+pub fn encode_eof(coder: &mut dyn EntropyCoder, state: &mut CoderState, config: &Config) {
-    encode_bit(coder, state, 0, true);
+    encode_bit(
-    if !state.prev_was_match {
+        coder,
-        encode_bit(coder, state, 256, true);
+        state,
+        state.pos % state.parity_contexts * 256,
+        config.is_match_bit,
+    );
+    if !state.prev_was_match && !config.no_repeated_offsets {
+        encode_bit(
+            coder,
+            state,
+            256 * state.parity_contexts,
+            config.new_offset_bit ^ config.eof_in_length,
+        );
+    }
+    if !config.eof_in_length || state.prev_was_match || config.no_repeated_offsets {
+        encode_length(coder, state, 256 * state.parity_contexts + 1, 1, config);
+    }
+    if config.eof_in_length {
+        encode_length(coder, state, 256 * state.parity_contexts + 65, 1, config);
     }
-    encode_length(coder, state, 257, 1);
 }
 
 fn encode_bit(
@@ -60,17 +93,18 @@ fn encode_length(
     state: &mut CoderState,
     context_start: usize,
     mut value: u32,
+    config: &Config,
 ) {
     assert!(value >= 1);
 
     let mut context_index = context_start;
     while value >= 2 {
-        encode_bit(coder, state, context_index, true);
+        encode_bit(coder, state, context_index, config.continue_value_bit);
         encode_bit(coder, state, context_index + 1, value & 1 != 0);
         context_index += 2;
         value >>= 1;
     }
-    encode_bit(coder, state, context_index, false);
+    encode_bit(coder, state, context_index, !config.continue_value_bit);
 }
 
 #[derive(Clone)]
@@ -78,14 +112,18 @@ pub struct CoderState {
     contexts: ContextState,
     last_offset: u32,
     prev_was_match: bool,
+    pos: usize,
+    parity_contexts: usize,
 }
 
 impl CoderState {
-    pub fn new() -> CoderState {
+    pub fn new(config: &Config) -> CoderState {
         CoderState {
-            contexts: ContextState::new(1 + 255 + 1 + 64 + 64),
+            contexts: ContextState::new((1 + 255) * config.parity_contexts + 1 + 64 + 64, config),
             last_offset: 0,
             prev_was_match: false,
+            pos: 0,
+            parity_contexts: config.parity_contexts,
         }
     }
 
@@ -94,55 +132,141 @@ impl CoderState {
     }
 }
 
-pub fn unpack(packed_data: &[u8], use_bitstream: bool) -> Vec<u8> {
+#[derive(Error, Debug)]
-    let mut decoder = RansDecoder::new(packed_data, use_bitstream);
+pub enum UnpackError {
-    let mut contexts = ContextState::new(1 + 255 + 1 + 64 + 64);
+    #[error("match offset out of range: {offset} > {position}")]
+    OffsetOutOfRange { offset: usize, position: usize },
+    #[error("Unpacked data over size limit: {size} > {limit}")]
+    OverSize { size: usize, limit: usize },
+    #[error("Unexpected end of input data")]
+    UnexpectedEOF {
+        #[from]
+        source: crate::rans::UnexpectedEOF,
+    },
+    #[error("Overflow while reading value")]
+    ValueOverflow,
+}
+
+pub fn unpack(
+    packed_data: &[u8],
+    config: &Config,
+    max_size: usize,
+) -> Result<Vec<u8>, UnpackError> {
     let mut result = vec![];
-    let mut offset = 0;
+    let _ = unpack_internal(Some(&mut result), packed_data, config, max_size)?;
+    Ok(result)
+}
+
+pub fn calculate_margin(packed_data: &[u8], config: &Config) -> Result<isize, UnpackError> {
+    unpack_internal(None, packed_data, config, usize::MAX)
+}
+
+pub fn unpack_internal(
+    mut result: Option<&mut Vec<u8>>,
+    packed_data: &[u8],
+    config: &Config,
+    max_size: usize,
+) -> Result<isize, UnpackError> {
+    let mut decoder = RansDecoder::new(packed_data, &config);
+    let mut contexts = ContextState::new((1 + 255) * config.parity_contexts + 1 + 64 + 64, &config);
+    let mut offset = usize::MAX;
+    let mut position = 0usize;
     let mut prev_was_match = false;
+    let mut margin = 0isize;
 
     fn decode_length(
         decoder: &mut RansDecoder,
         contexts: &mut ContextState,
         mut context_index: usize,
-    ) -> usize {
+        config: &Config,
+    ) -> Result<usize, UnpackError> {
         let mut length = 0;
         let mut bit_pos = 0;
-        while decoder.decode_with_context(&mut contexts.context_mut(context_index)) {
+        while decoder.decode_with_context(&mut contexts.context_mut(context_index))?
-            length |= (decoder.decode_with_context(&mut contexts.context_mut(context_index + 1))
+            == config.continue_value_bit
+        {
+            length |= (decoder.decode_with_context(&mut contexts.context_mut(context_index + 1))?
                 as usize)
                 << bit_pos;
             bit_pos += 1;
+            if bit_pos >= 32 {
+                return Err(UnpackError::ValueOverflow);
+            }
             context_index += 2;
         }
-        length | (1 << bit_pos)
+        Ok(length | (1 << bit_pos))
     }
 
     loop {
-        if decoder.decode_with_context(&mut contexts.context_mut(0)) {
+        margin = margin.max(position as isize - decoder.pos() as isize);
-            if prev_was_match || decoder.decode_with_context(&mut contexts.context_mut(256)) {
+        let literal_base = position % config.parity_contexts * 256;
-                offset = decode_length(&mut decoder, &mut contexts, 257) - 1;
+        if decoder.decode_with_context(&mut contexts.context_mut(literal_base))?
+            == config.is_match_bit
+        {
+            if config.no_repeated_offsets
+                || prev_was_match
+                || decoder
+                    .decode_with_context(&mut contexts.context_mut(256 * config.parity_contexts))?
+                    == config.new_offset_bit
+            {
+                offset = decode_length(
+                    &mut decoder,
+                    &mut contexts,
+                    256 * config.parity_contexts + 1,
+                    &config,
+                )? - if config.eof_in_length { 0 } else { 1 };
                 if offset == 0 {
                     break;
                 }
             }
-            let length = decode_length(&mut decoder, &mut contexts, 257 + 64);
+            let length = decode_length(
-            for _ in 0..length {
+                &mut decoder,
-                result.push(result[result.len() - offset]);
+                &mut contexts,
+                256 * config.parity_contexts + 65,
+                &config,
+            )?;
+            if config.eof_in_length && length == 1 {
+                break;
             }
+            if offset > position {
+                return Err(UnpackError::OffsetOutOfRange { offset, position });
+            }
+            if let Some(ref mut result) = result {
+                for _ in 0..length {
+                    if result.len() < max_size {
+                        result.push(result[result.len() - offset]);
+                    } else {
+                        break;
+                    }
+                }
+            }
+            position += length;
             prev_was_match = true;
         } else {
             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;
             }
-            result.push(byte);
+            if let Some(ref mut result) = result {
+                if result.len() < max_size {
+                    result.push(byte);
+                }
+            }
+            position += 1;
             prev_was_match = false;
         }
     }
 
-    result
+    if position > max_size {
+        return Err(UnpackError::OverSize {
+            size: position,
+            limit: max_size,
+        });
+    }
+
+    Ok(margin + decoder.pos() as isize - position as isize)
 }

src/main.rs

@@ -1,67 +1,175 @@
-use anyhow::{bail, Result};
+use anyhow::Result;
+use std::ffi::OsStr;
 use std::io::prelude::*;
+use std::process;
 use std::{fs::File, path::PathBuf};
 
 fn main() -> Result<()> {
-    let mut args = pico_args::Arguments::from_env();
+    let mut config = upkr::Config::default();
+    let mut reverse = false;
+    let mut unpack = false;
+    let mut calculate_margin = false;
+    let mut level = 2;
+    let mut infile: Option<PathBuf> = None;
+    let mut outfile: Option<PathBuf> = None;
+    let mut max_unpacked_size = 512 * 1024 * 1024;
 
-    match args.subcommand()?.as_ref().map(|s| s.as_str()) {
+    let mut parser = lexopt::Parser::from_env();
-        None => print_help(),
+    while let Some(arg) = parser.next()? {
-        Some("pack") => {
+        use lexopt::prelude::*;
-            let level = args.opt_value_from_str(["-l", "--level"])?.unwrap_or(2u8);
+        match arg {
-            let use_bitstream = args.contains(["-b", "--bitstream"]);
+            Short('b') | Long("bitstream") => config.use_bitstream = true,
+            Short('p') | Long("parity") => config.parity_contexts = parser.value()?.parse()?,
+            Short('r') | Long("reverse") => reverse = true,
+            Long("invert-is-match-bit") => config.is_match_bit = false,
+            Long("invert-new-offset-bit") => config.new_offset_bit = false,
+            Long("invert-continue-value-bit") => config.continue_value_bit = false,
+            Long("invert-bit-encoding") => config.invert_bit_encoding = true,
+            Long("simplified-prob-update") => config.simplified_prob_update = true,
+            Long("big-endian-bitstream") => {
+                config.use_bitstream = true;
+                config.bitstream_is_big_endian = true;
+            }
+            Long("no-repeated-offsets") => config.no_repeated_offsets = true,
+            Long("eof-in-length") => config.eof_in_length = true,
 
-            let infile = args.free_from_os_str::<PathBuf, bool>(|s| Ok(s.into()))?;
+            Long("max-offset") => config.max_offset = parser.value()?.parse()?,
-            let outfile = args.free_from_os_str::<PathBuf, bool>(|s| Ok(s.into()))?;
+            Long("max-length") => config.max_length = parser.value()?.parse()?,
 
-            let mut data = vec![];
+            Long("z80") => {
-            File::open(infile)?.read_to_end(&mut data)?;
+                config.use_bitstream = true;
+                config.bitstream_is_big_endian = true;
+                config.invert_bit_encoding = true;
+                config.simplified_prob_update = true;
+                level = 9;
+            }
+            Long("x86") => {
+                config.use_bitstream = true;
+                config.continue_value_bit = false;
+                config.is_match_bit = false;
+                config.new_offset_bit = false;
+            }
 
-            let mut pb = pbr::ProgressBar::new(data.len() as u64);
+            Short('u') | Long("unpack") => unpack = true,
-            pb.set_units(pbr::Units::Bytes);
+            Long("margin") => calculate_margin = true,
-            let packed_data = upkr::pack(
+            Short('l') | Long("level") => level = parser.value()?.parse()?,
-                &data,
+            Short(n) if n.is_ascii_digit() => level = n as u8 - b'0',
-                level,
+            Short('h') | Long("help") => print_help(0),
-                use_bitstream,
+            Long("max-unpacked-size") => max_unpacked_size = parser.value()?.parse()?,
-                Some(&mut |pos| {
+            Value(val) if infile.is_none() => infile = Some(val.try_into()?),
-                    pb.set(pos as u64);
+            Value(val) if outfile.is_none() => outfile = Some(val.try_into()?),
-                }),
+            _ => return Err(arg.unexpected().into()),
-            );
-            pb.finish();
-
-            println!(
-                "Compressed {} bytes to {} bytes ({}%)",
-                data.len(),
-                packed_data.len(),
-                packed_data.len() as f32 * 100. / data.len() as f32
-            );
-            File::create(outfile)?.write_all(&packed_data)?;
         }
-        Some("unpack") => {
+    }
-            let use_bitstream = args.contains(["-b", "--bitstream"]);
 
-            let infile = args.free_from_os_str::<PathBuf, bool>(|s| Ok(s.into()))?;
+    let infile = infile.unwrap_or_else(|| print_help(1));
-            let outfile = args.free_from_os_str::<PathBuf, bool>(|s| Ok(s.into()))?;
+    let outfile = outfile.unwrap_or_else(|| {
-
+        let mut name = infile.clone();
-            let mut data = vec![];
+        if unpack {
-            File::open(infile)?.read_to_end(&mut data)?;
+            if name.extension().filter(|&e| e == "upk").is_some() {
-            let packed_data = upkr::unpack(&data, use_bitstream);
+                name.set_extension("");
-            File::create(outfile)?.write_all(&packed_data)?;
+            } else {
+                name.set_extension("bin");
+            }
+        } else {
+            let mut filename = name
+                .file_name()
+                .unwrap_or_else(|| OsStr::new(""))
+                .to_os_string();
+            filename.push(".upk");
+            name.set_file_name(filename);
         }
-        Some(other) => {
+        name
-            bail!("Unknown subcommand '{}'", other);
+    });
+
+    if config.parity_contexts != 1 && config.parity_contexts != 2 && config.parity_contexts != 4 {
+        eprintln!("--parity has to be 1, 2, or 4");
+        process::exit(1);
+    }
+
+    if !unpack && !calculate_margin {
+        let mut data = vec![];
+        File::open(infile)?.read_to_end(&mut data)?;
+        if reverse {
+            data.reverse();
+        }
+
+        let mut pb = pbr::ProgressBar::new(data.len() as u64);
+        pb.set_units(pbr::Units::Bytes);
+        let mut packed_data = upkr::pack(
+            &data,
+            level,
+            &config,
+            Some(&mut |pos| {
+                pb.set(pos as u64);
+            }),
+        );
+        pb.finish();
+
+        if reverse {
+            packed_data.reverse();
+        }
+
+        println!(
+            "Compressed {} bytes to {} bytes ({}%)",
+            data.len(),
+            packed_data.len(),
+            packed_data.len() as f32 * 100. / data.len() as f32
+        );
+        File::create(outfile)?.write_all(&packed_data)?;
+    } else {
+        let mut data = vec![];
+        File::open(infile)?.read_to_end(&mut data)?;
+        if reverse {
+            data.reverse();
+        }
+        if unpack {
+            let mut unpacked_data = upkr::unpack(&data, &config, max_unpacked_size)?;
+            if reverse {
+                unpacked_data.reverse();
+            }
+            File::create(outfile)?.write_all(&unpacked_data)?;
+        }
+        if calculate_margin {
+            println!("{}", upkr::calculate_margin(&data, &config)?);
         }
     }
 
     Ok(())
 }
 
-fn print_help() {
+fn print_help(exit_code: i32) -> ! {
     eprintln!("Usage:");
-    eprintln!("  upkr pack [-b] [-l level(0-9)] <infile> <outfile>");
+    eprintln!("  upkr [-l level(0-9)] [config options] <infile> [<outfile>]");
-    eprintln!("  upkr unpack [-b] <infile> <outfile>");
+    eprintln!("  upkr -u [config options] <infile> [<outfile>]");
+    eprintln!("  upkr --margin [config options] <infile>");
     eprintln!();
-    eprintln!(" -b, --bitstream     bitstream mode");
     eprintln!(" -l, --level N       compression level 0-9");
-    std::process::exit(1);
+    eprintln!(" -0, ..., -9         short form for setting compression level");
+    eprintln!(" -u, --unpack        unpack infile");
+    eprintln!(" --margin            calculate margin for overlapped unpacking of a packed file");
+    eprintln!();
+    eprintln!("Config presets for specific unpackers:");
+    eprintln!(" --z80               --big-endian-bitstream --invert-bit-encoding --simplified-prob-update -9");
+    eprintln!(
+        " --x86               --bitstream --invert-is-match-bit --invert-continue-value-bit --invert-new-offset-bit"
+    );
+    eprintln!();
+    eprintln!("Config options (need to match when packing/unpacking):");
+    eprintln!(" -b, --bitstream     bitstream mode");
+    eprintln!(" -p, --parity N      use N (2/4) parity contexts");
+    eprintln!(" -r, --reverse       reverse input & output");
+    eprintln!();
+    eprintln!("Config options to tailor output to specific optimized unpackers:");
+    eprintln!(" --invert-is-match-bit");
+    eprintln!(" --invert-new-offset-bit");
+    eprintln!(" --invert-continue-value-bit");
+    eprintln!(" --invert-bit-encoding");
+    eprintln!(" --simplified-prob-update");
+    eprintln!(" --big-endian-bitstream   (implies --bitstream)");
+    eprintln!(" --no-repeated-offsets");
+    eprintln!(" --eof-in-length");
+    eprintln!(" --max-offset N");
+    eprintln!(" --max-length N");
+    process::exit(exit_code);
 }

src/parsing_packer.rs

@@ -6,19 +6,24 @@ use crate::match_finder::MatchFinder;
 use crate::rans::{CostCounter, RansCoder};
 use crate::{lz, ProgressCallback};
 
-pub fn pack(data: &[u8], level: u8, use_bitstream: bool, progress_cb: Option<ProgressCallback>) -> Vec<u8> {
+pub fn pack(
-    let mut parse = parse(data, Config::from_level(level), progress_cb);
+    data: &[u8],
+    level: u8,
+    config: &crate::Config,
+    progress_cb: Option<ProgressCallback>,
+) -> Vec<u8> {
+    let mut parse = parse(data, Config::from_level(level), config, 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();
+    let mut state = lz::CoderState::new(config);
-    let mut coder = RansCoder::new(use_bitstream);
+    let mut coder = RansCoder::new(config);
     for op in ops.into_iter().rev() {
-        op.encode(&mut coder, &mut state);
+        op.encode(&mut coder, &mut state, config);
     }
-    lz::encode_eof(&mut coder, &mut state);
+    lz::encode_eof(&mut coder, &mut state, config);
     coder.finish()
 }
 
@@ -38,6 +43,7 @@ type Arrivals = HashMap<usize, Vec<Arrival>>;
 fn parse(
     data: &[u8],
     config: Config,
+    encoding_config: &crate::Config,
     mut progress_cb: Option<ProgressCallback>,
 ) -> Option<Rc<Parse>> {
     let mut match_finder = MatchFinder::new(data)
@@ -99,17 +105,22 @@ fn parse(
         cost_counter: &mut CostCounter,
         pos: usize,
         offset: usize,
-        length: usize,
+        mut length: usize,
         arrival: &Arrival,
         max_arrivals: usize,
+        config: &crate::Config,
     ) {
+        if length < config.min_length() {
+            return;
+        }
+        length = length.min(config.max_length);
         cost_counter.reset();
         let mut state = arrival.state.clone();
         let op = lz::Op::Match {
             offset: offset as u32,
             len: length as u32,
         };
-        op.encode(cost_counter, &mut state);
+        op.encode(cost_counter, &mut state, config);
         add_arrival(
             arrivals,
             pos + length,
@@ -129,13 +140,13 @@ fn parse(
         0,
         Arrival {
             parse: None,
-            state: lz::CoderState::new(),
+            state: lz::CoderState::new(encoding_config),
             cost: 0.0,
         },
         max_arrivals,
     );
 
-    let cost_counter = &mut CostCounter::new();
+    let cost_counter = &mut CostCounter::new(encoding_config);
     let mut best_per_offset = HashMap::new();
     for pos in 0..data.len() {
         let match_length = |offset: usize| {
@@ -176,18 +187,21 @@ fn parse(
             for m in match_finder.matches(pos) {
                 closest_match = Some(closest_match.unwrap_or(0).max(m.pos));
                 let offset = pos - m.pos;
-                found_last_offset |= offset as u32 == arrival.state.last_offset();
+                if offset <= encoding_config.max_offset {
-                add_match(
+                    found_last_offset |= offset as u32 == arrival.state.last_offset();
-                    &mut arrivals,
+                    add_match(
-                    cost_counter,
+                        &mut arrivals,
-                    pos,
+                        cost_counter,
-                    offset,
+                        pos,
-                    m.length,
+                        offset,
-                    &arrival,
+                        m.length,
-                    max_arrivals,
+                        &arrival,
-                );
+                        max_arrivals,
-                if m.length >= config.greedy_size {
+                        encoding_config,
-                    break 'arrival_loop;
+                    );
+                    if m.length >= config.greedy_size {
+                        break 'arrival_loop;
+                    }
                 }
             }
 
@@ -198,6 +212,9 @@ fn parse(
                 && closest_match.iter().all(|p| *p < match_pos)
             {
                 let offset = pos - match_pos;
+                if offset > encoding_config.max_offset {
+                    break;
+                }
                 let length = match_length(offset);
                 assert!(length > 0);
                 add_match(
@@ -208,6 +225,7 @@ fn parse(
                     length,
                     &arrival,
                     max_arrivals,
+                    encoding_config,
                 );
                 found_last_offset |= offset as u32 == arrival.state.last_offset();
                 if offset < near_matches.len() {
@@ -228,6 +246,7 @@ fn parse(
                         length,
                         &arrival,
                         max_arrivals,
+                        encoding_config,
                     );
                 }
             }
@@ -235,7 +254,7 @@ fn parse(
             cost_counter.reset();
             let mut state = arrival.state;
             let op = lz::Op::Literal(data[pos]);
-            op.encode(cost_counter, &mut state);
+            op.encode(cost_counter, &mut state, encoding_config);
             add_arrival(
                 &mut arrivals,
                 pos + 1,

src/rans.rs

@@ -1,4 +1,5 @@
-use crate::context_state::Context;
+use crate::{context_state::Context, Config};
+use thiserror::Error;
 
 pub const PROB_BITS: u32 = 8;
 pub const ONE_PROB: u32 = 1 << PROB_BITS;
@@ -15,20 +16,25 @@ pub trait EntropyCoder {
 pub struct RansCoder {
     bits: Vec<u16>,
     use_bitstream: bool,
+    bitstream_is_big_endian: bool,
+    invert_bit_encoding: bool,
 }
 
 impl EntropyCoder for RansCoder {
     fn encode_bit(&mut self, bit: bool, prob: u16) {
         assert!(prob < 32768);
-        self.bits.push(prob | ((bit as u16) << 15));
+        self.bits
+            .push(prob | (((bit ^ self.invert_bit_encoding) as u16) << 15));
     }
 }
 
 impl RansCoder {
-    pub fn new(use_bitstream: bool) -> RansCoder {
+    pub fn new(config: &Config) -> RansCoder {
         RansCoder {
             bits: Vec::new(),
-            use_bitstream,
+            use_bitstream: config.use_bitstream,
+            bitstream_is_big_endian: config.bitstream_is_big_endian,
+            invert_bit_encoding: config.invert_bit_encoding,
         }
     }
 
@@ -38,18 +44,31 @@ impl RansCoder {
         let mut state = 1 << l_bits;
 
         let mut byte = 0u8;
-        let mut bit = 0;
+        let mut bit = if self.bitstream_is_big_endian { 0 } else { 8 };
         let mut flush_state: Box<dyn FnMut(&mut u32)> = if self.use_bitstream {
-            Box::new(|state: &mut u32| {
+            if self.bitstream_is_big_endian {
-                byte |= ((*state & 1) as u8) << bit;
+                Box::new(|state: &mut u32| {
-                bit += 1;
+                    byte |= ((*state & 1) as u8) << bit;
-                if bit == 8 {
+                    bit += 1;
-                    buffer.push(byte);
+                    if bit == 8 {
-                    byte = 0;
+                        buffer.push(byte);
-                    bit = 0;
+                        byte = 0;
-                }
+                        bit = 0;
-                *state >>= 1;
+                    }
-            })
+                    *state >>= 1;
+                })
+            } else {
+                Box::new(|state: &mut u32| {
+                    bit -= 1;
+                    byte |= ((*state & 1) as u8) << bit;
+                    if bit == 0 {
+                        buffer.push(byte);
+                        byte = 0;
+                        bit = 8;
+                    }
+                    *state >>= 1;
+                })
+            }
         } else {
             Box::new(|state: &mut u32| {
                 buffer.push(*state as u8);
@@ -61,7 +80,7 @@ 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)
@@ -91,10 +110,11 @@ impl RansCoder {
 pub struct CostCounter {
     cost: f64,
     log2_table: Vec<f64>,
+    invert_bit_encoding: bool,
 }
 
 impl CostCounter {
-    pub fn new() -> CostCounter {
+    pub fn new(config: &Config) -> CostCounter {
         let log2_table = (0..ONE_PROB)
             .map(|prob| {
                 let inv_prob = ONE_PROB as f64 / prob as f64;
@@ -104,6 +124,7 @@ impl CostCounter {
         CostCounter {
             cost: 0.0,
             log2_table,
+            invert_bit_encoding: config.invert_bit_encoding,
         }
     }
 
@@ -118,7 +139,7 @@ impl CostCounter {
 
 impl EntropyCoder for CostCounter {
     fn encode_bit(&mut self, bit: bool, prob: u16) {
-        let prob = if !bit {
+        let prob = if bit ^ self.invert_bit_encoding {
             prob as u32
         } else {
             ONE_PROB - prob as u32
@@ -129,60 +150,85 @@ impl EntropyCoder for CostCounter {
 
 pub struct RansDecoder<'a> {
     data: &'a [u8],
+    pos: usize,
     state: u32,
     use_bitstream: bool,
     byte: u8,
     bits_left: u8,
+    invert_bit_encoding: bool,
+    bitstream_is_big_endian: bool,
 }
 
 const PROB_MASK: u32 = ONE_PROB - 1;
 
+#[derive(Debug, Error)]
+#[error("Unexpected end of input")]
+pub struct UnexpectedEOF;
+
 impl<'a> RansDecoder<'a> {
-    pub fn new(data: &'a [u8], use_bitstream: bool) -> RansDecoder<'a> {
+    pub fn new(data: &'a [u8], config: &Config) -> RansDecoder<'a> {
         RansDecoder {
             data,
+            pos: 0,
             state: 0,
-            use_bitstream,
+            use_bitstream: config.use_bitstream,
             byte: 0,
             bits_left: 0,
+            invert_bit_encoding: config.invert_bit_encoding,
+            bitstream_is_big_endian: config.bitstream_is_big_endian,
         }
     }
 
-    pub fn decode_with_context(&mut self, context: &mut Context) -> bool {
+    pub fn pos(&self) -> usize {
-        let bit = self.decode_bit(context.prob());
+        self.pos
-        context.update(bit);
-        bit
     }
 
-    pub fn decode_bit(&mut self, prob: u16) -> bool {
+    pub fn decode_with_context(&mut self, context: &mut Context) -> Result<bool, UnexpectedEOF> {
+        let bit = self.decode_bit(context.prob())?;
+        context.update(bit);
+        Ok(bit)
+    }
+
+    pub fn decode_bit(&mut self, prob: u16) -> Result<bool, UnexpectedEOF> {
         let prob = prob as u32;
         if self.use_bitstream {
             while self.state < 32768 {
                 if self.bits_left == 0 {
-                    self.byte = self.data[0];
+                    if self.pos >= self.data.len() {
-                    self.data = &self.data[1..];
+                        return Err(UnexpectedEOF);
+                    }
+                    self.byte = self.data[self.pos];
+                    self.pos += 1;
                     self.bits_left = 8;
                 }
-                self.state = (self.state << 1) | (self.byte >> 7) as u32;
+                if self.bitstream_is_big_endian {
-                self.byte <<= 1;
+                    self.state = (self.state << 1) | (self.byte >> 7) as u32;
+                    self.byte <<= 1;
+                } else {
+                    self.state = (self.state << 1) | (self.byte & 1) as u32;
+                    self.byte >>= 1;
+                }
                 self.bits_left -= 1;
             }
         } else {
             while self.state < 4096 {
-                self.state = (self.state << 8) | self.data[0] as u32;
+                if self.pos >= self.data.len() {
-                self.data = &self.data[1..];
+                    return Err(UnexpectedEOF);
+                }
+                self.state = (self.state << 8) | self.data[self.pos] as u32;
+                self.pos += 1;
             }
         }
 
-        let bit = (self.state & PROB_MASK) >= prob;
+        let bit = (self.state & PROB_MASK) < prob;
 
         let (start, prob) = if bit {
-            (prob, ONE_PROB - prob)
-        } else {
             (0, prob)
+        } else {
+            (prob, ONE_PROB - prob)
         };
         self.state = prob * (self.state >> PROB_BITS) + (self.state & PROB_MASK) - start;
 
-        bit
+        Ok(bit ^ self.invert_bit_encoding)
     }
 }

z80_unpacker/.gitignore

@@ -1,4 +1,3 @@
 *.bin
 *.tap
-*.sna
 *.lst

z80_unpacker/example/example.asm

@@ -3,7 +3,8 @@
     DEVICE ZXSPECTRUM48,$8FFF
 
     ORG     $9000
-compressed_scr_files:       ; border color byte + upkr-packed .scr file
+  ;; forward example data
+compressed_scr_files.fwd:               ; border color byte + upkr-packed .scr file
     DB      1
     INCBIN  "screens/Grongy - ZX Spectrum (2022).scr.upk"
     DB      7
@@ -13,37 +14,87 @@ compressed_scr_files:       ; border color byte + upkr-packed .scr file
     DB      6
     INCBIN  "screens/diver - Back to Bjork (2015).scr.upk"
 .e:
+  ;; backward example data (unpacker goes from the end of the data!)
+compressed_scr_files.rwd.e: EQU $-1     ; the final IX will point one byte ahead of "$" here
+    INCBIN  "screens.reversed/diver - Back to Bjork (2015).scr.upk"
+    DB      6
+    INCBIN  "screens.reversed/diver - Mercenary 4. The Heaven's Devil (2014) (Forever 2014 Olympic Edition, 1).scr.upk"
+    DB      0
+    INCBIN  "screens.reversed/Schafft - Poison (2017).scr.upk"
+    DB      7
+    INCBIN  "screens.reversed/Grongy - ZX Spectrum (2022).scr.upk"
+compressed_scr_files.rwd:               ; border color byte + upkr-packed .scr file (backward)
+    DB      1
 
 start:
     di
 ;     OPT --zxnext
-;     nextreg 7,3                 ; ZX Next: switch to 28Mhz
+;     nextreg 7,3                       ; ZX Next: switch to 28Mhz
-    ld      ix,compressed_scr_files
+
-.slideshow_loop
+  ;;; FORWARD packed/unpacked data demo
+    ld      ix,compressed_scr_files.fwd
+.slideshow_loop.fwd:
   ; set BORDER for next image
-    ldi     a,(ix)              ; fake: ld a,(ix) : inc ix
+    ld      a,(ix)
+    inc     ix
     out     (254),a
   ; call unpack of next image directly into VRAM
-    ld      de,$4000            ; target VRAM
+    ld      de,$4000                    ; target VRAM
     exx
   ; IX = packed data, DE' = destination ($4000)
   ; returned IX will point right after the packed data
-    call    upkr.unpack
+    call    fwd.upkr.unpack
   ; do some busy loop with CPU to delay between images
+    call    delay
+  ; check if all images were displayed, loop around from first one then
+    ld      a,ixl
+    cp      low compressed_scr_files.fwd.e
+    jr      nz,.slideshow_loop.fwd
+
+  ;;; BACKWARD packed/unpacked data demo
+    ld      ix,compressed_scr_files.rwd
+.slideshow_loop.rwd:
+  ; set BORDER for next image
+    ld      a,(ix)
+    dec     ix
+    out     (254),a
+  ; call unpack of next image directly into VRAM
+    ld      de,$5AFF                    ; target VRAM
+    exx
+  ; IX = packed data, DE' = destination
+  ; returned IX will point right ahead of the packed data
+    call    rwd.upkr.unpack
+  ; do some busy loop with CPU to delay between images
+    call    delay
+  ; check if all images were displayed, loop around from first one then
+    ld      a,ixl
+    cp      low compressed_scr_files.rwd.e
+    jr      nz,.slideshow_loop.rwd
+
+    jr      start
+
+delay:
     ld      bc,$AA00
 .delay:
     .8 ex      (sp),ix
     dec     c
     jr      nz,.delay
     djnz    .delay
-  ; check if all images were displayed, loop around from first one then
+    ret
-    ld      a,ixl
-    cp      low compressed_scr_files.e
-    jr      z,start
-    jr      .slideshow_loop
 
   ; include the depacker library, optionally putting probs array buffer near end of RAM
     DEFINE  UPKR_PROBS_ORIGIN $FA00   ; if not defined, array will be put after unpack code
-    INCLUDE "../unpack.asm"
+
+    MODULE fwd
+        INCLUDE "../unpack.asm"
+    ENDMODULE
+
+    MODULE rwd
+        DEFINE BACKWARDS_UNPACK         ; defined to build backwards unpack
+                ; initial IX points at last byte of compressed data
+                ; initial DE' points at last byte of unpacked data
+
+        INCLUDE "../unpack.asm"
+    ENDMODULE
 
     SAVESNA "example.sna",start

z80_unpacker/readme.txt

@@ -10,10 +10,23 @@ may be incompatible with files you will produce with current version)
 
 Asm syntax is z00m's sjasmplus: https://github.com/z00m128/sjasmplus
 
+Backward direction unpacker added as compile-time option, see example for both forward/backward
+depacker in action.
+
+The packed/unpacked data-overlap has to be tested per-case, in worst case the packed data
+may need even more than 7 bytes to unpack final byte, but usually 1-4 bytes may suffice.
+
 TODO:
-- build base corpus of test data to benchmark future changes in algorithm/format
+- build bigger corpus of test data to benchmark future changes in algorithm/format (example and zx48.rom was used to do initial tests)
-- review first implementation to identify weak spots where the implementation can be shorter+faster
+- maybe try to beat double-loop `decode_number` with different encoding format
-with acceptable small changes to the format
-- review non-bitstream variant, if it's feasible to try to implement it with Z80
 - (@ped7g) Z80N version of unpacker for ZX Next devs
 - (@exoticorn) add Z80 specific packer (to avoid confusion with original MicroW8 variant), and land it all to master branch, maybe in "z80" directory or something? (and overall decide how to organise+merge this upstream into main repo)
+- (@exoticorn) add to packer output with possible packed/unpacked region overlap
+
+DONE:
+* review non-bitstream variant, if it's feasible to try to implement it with Z80
+    - Ped7g: IMHO nope, the 12b x 8b MUL code would probably quickly cancel any gains from the simpler state update
+* review first implementation to identify weak spots where the implementation can be shorter+faster
+with acceptable small changes to the format
+    - Ped7g: the decode_bit settled down and now doesn't feel so confused and redundant, the code seems pretty on point to me, no obvious simplification from format change
+    - Ped7g: the decode_number double-loop is surprisingly resilient, especially in terms of code size I failed to beat it, speed wise only negligible gains

z80_unpacker/unpack.asm

@@ -4,7 +4,7 @@
 ;; initial version by Peter "Ped" Helcmanovsky (C) 2022, licensed same as upkr project ("unlicensed")
 ;; to assemble use z00m's sjasmplus: https://github.com/z00m128/sjasmplus
 ;;
-;; you can define UPKR_PROBS_ORIGIN to specific 256 byte aligned address for probs array (386 bytes),
+;; you can define UPKR_PROBS_ORIGIN to specific 256 byte aligned address for probs array (320 bytes),
 ;; otherwise it will be positioned after the unpacker code (256 aligned)
 ;;
 ;; public API:
@@ -12,12 +12,24 @@
 ;;     upkr.unpack
 ;;         IN: IX = packed data, DE' (shadow DE) = destination
 ;;         OUT: IX = after packed data
-;;         modifies: all registers except IY, requires 14 bytes of stack space
+;;         modifies: all registers except IY, requires 10 bytes of stack space
 ;;
 
+;     DEFINE BACKWARDS_UNPACK         ; uncomment to build backwards depacker (write_ptr--, upkr_data_ptr--)
+            ; initial IX points at last byte of compressed data
+            ; initial DE' points at last byte of unpacked data
+
+;     DEFINE UPKR_UNPACK_SPEED        ; uncomment to get larger but faster unpack routine
+
+; code size hint: if you put probs array just ahead of BASIC entry point, you will get BC
+; initialised to probs.e by BASIC `USR` command and you can remove it from unpack init (-3B)
+
     OPT push reset --syntax=abf
     MODULE upkr
 
+NUMBER_BITS     EQU     16+15       ; context-bits per offset/length (16+15 for 16bit offsets/pointers)
+    ; numbers (offsets/lengths) are encoded like: 1a1b1c1d1e0 = 0000'0000'001e'dbca
+
 /*
 u8* upkr_data_ptr;
 u8 upkr_probs[1 + 255 + 1 + 2*32 + 2*32];
@@ -81,8 +93,8 @@ unpack:
     ; BC = probs (context_index 0), state HL = 0, A' = 0x80 (no source bits left in upkr_current_byte)
 
   ; ** main loop to decompress data
-.decompress_data_reset_match:
+    ; D = prev_was_match = uninitialised, literal is expected first => will reset D to "false"
-    ld      d,0                 ; prev_was_match = 0;
+    ; values for false/true of prev_was_match are: false = high(probs), true = 1 + high(probs)
 .decompress_data:
     ld      c,0
     call    decode_bit          ; if(upkr_decode_bit(0))
@@ -97,23 +109,23 @@ unpack:
     ld      a,c
     exx
     ld      (de),a              ; *write_ptr++ = byte;
-    inc     de
+    IFNDEF BACKWARDS_UNPACK : inc de : ELSE : dec de : ENDIF
     exx
-    jr      .decompress_data_reset_match
+    ld      d,b                 ; prev_was_match = false
+    jr      .decompress_data
 
   ; * copy chunk of already decompressed data (match)
 .copy_chunk:
+    ld      a,b
     inc     b                   ; context_index = 256
         ;             if(prev_was_match || upkr_decode_bit(256)) {
         ;                 offset = upkr_decode_length(257) - 1;
         ;                 if (0 == offset) break;
         ;             }
-    xor     a
     cp      d                   ; CF = prev_was_match
     call    nc,decode_bit       ; if not prev_was_match, then upkr_decode_bit(256)
     jr      nc,.keep_offset     ; if neither, keep old offset
-    inc     c
+    call    decode_number       ; context_index is already 257-1 as needed by decode_number
-    call    decode_length
     dec     de                  ; offset = upkr_decode_length(257) - 1;
     ld      a,d
     or      e
@@ -126,18 +138,27 @@ unpack:
         ;                 ++write_ptr;
         ;             }
         ;             prev_was_match = 1;
-    ld      c,low(257+64)       ; context_index = 257+64
+    ld      c,low(257 + NUMBER_BITS - 1)    ; context_index to second "number" set for lengths decoding
-    call    decode_length       ; length = upkr_decode_length(257 + 64);
+    call    decode_number       ; length = upkr_decode_length(257 + 64);
     push    de
     exx
-    ld      h,d                 ; DE = write_ptr
+    IFNDEF BACKWARDS_UNPACK
-    ld      l,e
+        ; forward unpack (write_ptr++, upkr_data_ptr++)
-.offset+*:  ld      bc,0
+        ld      h,d             ; DE = write_ptr
-    sbc     hl,bc               ; CF=0 from decode_length ; HL = write_ptr - offset
+        ld      l,e
-    pop     bc                  ; BC = length
+.offset+*:  ld  bc,0
-    ldir
+        sbc     hl,bc           ; CF=0 from decode_number ; HL = write_ptr - offset
+        pop     bc              ; BC = length
+        ldir
+    ELSE
+        ; backward unpack (write_ptr--, upkr_data_ptr--)
+.offset+*:  ld  hl,0
+        add     hl,de           ; HL = write_ptr + offset
+        pop     bc              ; BC = length
+        lddr
+    ENDIF
     exx
-    ld      d,b                 ; prev_was_match = non-zero
+    ld      d,b                 ; prev_was_match = true
     djnz    .decompress_data    ; adjust context_index back to 0..255 range, go to main loop
 
 /*
@@ -169,6 +190,9 @@ int upkr_decode_bit(int context_index) {
     return bit;
 }
 */
+inc_c_decode_bit:
+  ; ++low(context_index) before decode_bit (to get -1B by two calls in decode_number)
+    inc     c
 decode_bit:
   ; HL = upkr_state
   ; IX = upkr_data_ptr
@@ -189,7 +213,7 @@ decode_bit:
     jr      nz,.has_bit             ; CF=data, ZF=0 -> some bits + stop bit still available
   ; CF=1 (by stop bit)
     ld      a,(ix)
-    inc     ix                      ; upkr_current_byte = *upkr_data_ptr++;
+    IFNDEF BACKWARDS_UNPACK : inc ix : ELSE : dec ix : ENDIF    ; upkr_current_byte = *upkr_data_ptr++;
     adc     a,a                     ; CF=data, b0=1 as new stop bit
 .has_bit:
     adc     hl,hl                   ; upkr_state = (upkr_state << 1) + (upkr_current_byte >> 7);
@@ -202,9 +226,8 @@ decode_bit:
     cp      l                       ; CF = bit = prob-1 < (upkr_state & 255) <=> prob <= (upkr_state & 255)
     inc     a
   ; ** adjust state
-    push    af
+    push    bc
-    push    af
+    ld      c,l                     ; C = (upkr_state & 255); (preserving the value)
-    push    hl
     push    af
     jr      nc,.bit_is_0
     neg                             ; A = -prob == (256-prob), CF=1 preserved
@@ -212,38 +235,52 @@ decode_bit:
     ld      d,0
     ld      e,a                     ; DE = state_scale ; prob || (256-prob)
     ld      l,d                     ; H:L = (upkr_state>>8) : 0
-    ld      a,8                     ; counter
+
+  IFNDEF UPKR_UNPACK_SPEED
+
+    ;; looped MUL for minimum unpack size
+    ld      b,8                     ; counter
 .mulLoop:
     add     hl,hl
     jr      nc,.mul0
     add     hl,de
 .mul0:
-    dec     a
+    djnz    .mulLoop                ; until HL = state_scale * (upkr_state>>8), also BC becomes (upkr_state & 255)
-    jr      nz,.mulLoop             ; until HL = state_scale * (upkr_state>>8)
+
-    pop     af
+  ELSE
+
+    ;;; unrolled MUL for better performance, +25 bytes unpack size
+    ld      b,d
+    DUP     8
+        add     hl,hl
+        jr      nc,0_f
+        add     hl,de
+0:
+    EDUP
+
+  ENDIF
+
+    add     hl,bc                   ; HL = state_scale * (upkr_state >> 8) + (upkr_state & 255)
+    pop     af                      ; restore prob and CF=bit
     jr      nc,.bit_is_0_2
-    dec     d                       ; D = 0xFF (DE = -prob)
+    dec     d                       ; DE = -prob (also D = bit ? $FF : $00)
     add     hl,de                   ; HL += -prob
-.bit_is_0_2:                        ; HL = state_offset + state_scale * (upkr_state >> 8)
+    ; ^ this always preserves CF=1, because (state>>8) >= 128, state_scale: 7..250, prob: 7..250,
-    pop     de
+    ; so 7*128 > 250 and thus edge case `ADD hl=(7*128+0),de=(-250)` => CF=1
-    ld      d,0                     ; DE = (upkr_state & 255)
+.bit_is_0_2:
-    add     hl,de                   ; HL = state_offset + state_scale * (upkr_state >> 8) + (upkr_state & 255) ; new upkr_state
  ; *** adjust probs[context_index]
-    pop     af                      ; restore prob and bit
+    rra                             ; + (bit<<4) ; part of -prob_offset, needs another -16
+    and     $FC                     ; clear/keep correct bits to get desired (prob>>4) + extras, CF=0
+    rra
+    rra
+    rra                             ; A = (bit<<4) + (prob>>4), CF=(prob & 8)
+    adc     a,-16                   ; A = (bit<<4) - 16 + ((prob + 8)>>4) ; -prob_offset = (bit<<4) - 16
     ld      e,a
-    jr      c,.bit_is_1
+    pop     bc
-    ld      d,-16                   ; 0xF0
+    ld      a,(bc)                  ; A = prob (cheaper + shorter to re-read again from memory)
-.bit_is_1:                          ; D:E = -prob_offset:prob, A = prob
+    sub     e                       ; A = 16 - (bit<<4) + prob - ((prob + 8)>>4) ; = prob_offset + prob - ((prob + 8)>>4)
-    and     $F8
+    ld      (bc),a                  ; probs[context_index] = prob_offset + prob - ((prob + 8) >> 4);
-    rra
+    add     a,d                     ; restore CF = bit (D = bit ? $FF : $00 && A > 0)
-    rra
-    rra
-    rra
-    adc     a,d                     ; A = -prob_offset + ((prob + 8) >> 4)
-    neg
-    add     a,e                     ; A = prob_offset + prob - ((prob + 8) >> 4)
-    ld      (bc),a                  ; update probs[context_index]
-    pop     af                      ; restore resulting CF = bit
     pop     de
     ret
 
@@ -258,22 +295,19 @@ int upkr_decode_length(int context_index) {
     return length | (1 << bit_pos);
 }
 */
-decode_length:
+decode_number:
   ; HL = upkr_state
   ; IX = upkr_data_ptr
-  ; BC = probs+context_index
+  ; BC = probs+context_index-1
   ; A' = upkr_current_byte (!!! init to 0x80 at start, not 0x00)
   ; return length in DE, CF=0
-    ld      de,$7FFF            ; length = 0 with positional-stop-bit
+    ld      de,$FFFF            ; length = 0 with positional-stop-bit
-    jr      .loop_entry
+    or      a                   ; CF=0 to skip getting data bit and use only `rr d : rr e` to fix init DE
 .loop:
-    inc     c                   ; context_index + 1
+    call    c,inc_c_decode_bit  ; get data bit, context_index + 1 / if CF=0 just add stop bit into DE init
-    call    decode_bit
     rr      d
     rr      e                   ; DE = length = (length >> 1) | (bit << 15);
-    inc     c                   ; context_index += 2
+    call    inc_c_decode_bit    ; context_index += 2
-.loop_entry:
-    call    decode_bit
     jr      c,.loop
 .fix_bit_pos:
     ccf                         ; NC will become this final `| (1 << bit_pos)` bit
@@ -287,15 +321,61 @@ decode_length:
     ; reserve space for probs array without emitting any machine code (using only EQU)
 
     IFDEF UPKR_PROBS_ORIGIN     ; if specific address is defined by user, move probs array there
-    ORG UPKR_PROBS_ORIGIN
+probs:      EQU ((UPKR_PROBS_ORIGIN) + 255) & -$100     ; probs array aligned to 256
+    ELSE
+probs:      EQU ($ + 255) & -$100                       ; probs array aligned to 256
     ENDIF
-
+.real_c:    EQU 1 + 255 + 1 + 2*NUMBER_BITS             ; real size of probs array
-probs:      EQU ($+255) & -$100                 ; probs array aligned to 256
+.c:         EQU (.real_c + 1) & -2                      ; padding to even size (required by init code)
-.real_c:    EQU 1 + 255 + 1 + 2*32 + 2*32       ; real size of probs array
-.c:         EQU (.real_c + 1) & -2              ; padding to even size (required by init code)
 .e:         EQU probs + .c
 
     DISPLAY "upkr.unpack probs array placed at: ",/A,probs,",\tsize: ",/A,probs.c
 
+/*
+ archived: negligibly faster but +6B longer decode_number variant using HL' and BC' to
+ do `number|=(1<<bit_pos);` type of logic in single loop.
+*/
+; decode_number:
+;     exx
+;     ld      bc,1
+;     ld      l,b
+;     ld      h,b                 ; HL = 0
+; .loop
+;     exx
+;     inc     c
+;     call    decode_bit
+;     jr      nc,.done
+;     inc     c
+;     call    decode_bit
+;     exx
+;     jr      nc,.b0
+;     add     hl,bc
+; .b0:
+;     sla     c
+;     rl      b
+;     jr      .loop
+; .done:
+;     exx
+;     add     hl,bc
+;     push    hl
+;     exx
+;     pop     de
+;     ret
+
+/*
+ archived: possible LUT variant of updating probs value, requires 512-aligned 512B table (not tested)
+*/
+; code is replacing decode_bit from "; *** adjust probs[context_index]", followed by `ld (bc),a : add a,d ...`
+;     ld      c,a
+;     ld      a,high(probs_update_table)/2    ; must be 512 aligned
+;     rla
+;     ld      b,a
+;     ld      a,(bc)
+;     pop     bc
+; -------------------------------------------
+; probs_update_table: EQU probs-512
+; -------------------------------------------
+; table generator is not obvious and probably not short either, 20+ bytes almost for sure, maybe even 30-40
+
     ENDMODULE
     OPT pop