add --no-repeated-offsets to help

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "upkr"
-version = "0.2.0-pre1"
+version = "0.2.0-pre2"
 edition = "2021"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

src/lib.rs

@@ -20,6 +20,8 @@ pub struct Config {
 
     pub bitstream_is_big_endian: bool,
     pub simplified_prob_update: bool,
+
+    pub no_repeated_offsets: bool,
 }
 
 impl Default for Config {
@@ -35,6 +37,8 @@ impl Default for Config {
 
             bitstream_is_big_endian: false,
             simplified_prob_update: false,
+
+            no_repeated_offsets: false,
         }
     }
 }

src/lz.rs

@@ -25,7 +25,7 @@ impl Op {
             }
             &Op::Match { offset, len } => {
                 encode_bit(coder, state, literal_base, config.is_match_bit);
-                if !state.prev_was_match {
+                if !state.prev_was_match && !config.no_repeated_offsets {
                     encode_bit(
                         coder,
                         state,
@@ -33,9 +33,9 @@ impl Op {
                         (offset != state.last_offset) == config.new_offset_bit,
                     );
                 } else {
-                    assert!(offset != state.last_offset);
+                    assert!(offset != state.last_offset || config.no_repeated_offsets);
                 }
-                if offset != state.last_offset {
+                if offset != state.last_offset || config.no_repeated_offsets {
                     encode_length(
                         coder,
                         state,
@@ -156,7 +156,8 @@ pub fn unpack(packed_data: &[u8], config: Config) -> Vec<u8> {
         if decoder.decode_with_context(&mut contexts.context_mut(literal_base))
             == config.is_match_bit
         {
-            if prev_was_match
+            if config.no_repeated_offsets
+                || prev_was_match
                 || decoder
                     .decode_with_context(&mut contexts.context_mut(256 * config.parity_contexts))
                     == config.new_offset_bit

src/main.rs

@@ -28,6 +28,7 @@ fn main() -> Result<()> {
                 config.use_bitstream = true;
                 config.bitstream_is_big_endian = true;
             }
+            Long("no-repeated-offsets") => config.no_repeated_offsets = true,
 
             Long("z80") => {
                 config.use_bitstream = true;
@@ -145,5 +146,6 @@ fn print_help(exit_code: i32) -> ! {
     eprintln!(" --invert-bit-encoding");
     eprintln!(" --simplified-prob-update");
     eprintln!(" --big-endian-bitstream   (implies --bitstream)");
+    eprintln!(" --no-repeated-offsets");
     process::exit(exit_code);
 }