Merge #16

16: Do not raise error if code equals range in get_bit r=gendx a=dragly

It appears that code being equal to range is a valid state and that some files can have 
data encoded like this. An example of such a file has been added to the
tests.

### Pull Request Overview

This pull request fixes #15 

### Testing Strategy

This pull request was tested by...

- [ ] Added relevant unit tests.
- [x] Added relevant end-to-end tests (such as `.lzma`, `.lzma2`, `.xz` files).


### Supporting Documentation and References

The original data was produced by processing a randomly generated geometry with OpenCTM. OpenCTM files can contain embedded LZMA compressed data. This appears to be generated with the liblzma library. The data was then extracted to make a standalone file that is attached in this pull request.

### TODO or Help Wanted

None


Co-authored-by: Svenn-Arne Dragly <dragly@cognite.com>
Co-authored-by: gendx <gendx@users.noreply.github.com>
Co-authored-by: Svenn-Arne Dragly <s@dragly.com>

src/decode/rangecoder.rs

@@ -49,13 +49,7 @@ where
     fn get_bit(&mut self) -> error::Result<bool> {
         self.range >>= 1;
 
-        if self.code == self.range {
-            return Err(error::Error::LZMAError(String::from(
-                "Corrupted range coding",
-            )));
-        }
-
-        let bit = self.code > self.range;
+        let bit = self.code >= self.range;
         if bit {
             self.code -= self.range
         }

tests/files/README.md

@@ -0,0 +1,22 @@
+# Test files
+
+This folder contains a collection of test files to cover different use cases of the lzma-rs library.
+
+This README describes files that are not self-explanatory in this folder.
+
+## range-coder-edge-case
+
+This is a file that causes the code and range to be equal at some point during decoding LZMA data.
+Previously, this file would raise an `LZMAError("Corrupted range coding")`, although the file is a valid LZMA file.
+
+The file was created by generating random geometry in [Blender](1) using the Array and Build
+modifier on a cube.
+The geometry was then exported as an FBX file that was converted into OpenCTM using the 3D service
+in [Cognite Data Fusion](2).
+The vertices in the resulting OpenCTM file are LZMA-compressed.
+This LZMA-compressed section of the file was manually extracted and the header modified to include
+the unpacked size.
+The unpacked size is four times the vertex count found in the OpenCTM data.
+
+[1]: https://blender.org
+[2]: https://docs.cognite.com

tests/lzma.rs

@@ -92,13 +92,18 @@ fn round_trip_hello() {
 fn round_trip_files() {
     let _ = env_logger::try_init();
     round_trip_file("tests/files/foo.txt");
+    round_trip_file("tests/files/range-coder-edge-case");
 }
 
 #[test]
 fn big_file() {
     let _ = env_logger::try_init();
     decomp_big_file("tests/files/foo.txt.lzma", "tests/files/foo.txt");
     decomp_big_file("tests/files/hugedict.txt.lzma", "tests/files/foo.txt");
+    decomp_big_file(
+        "tests/files/range-coder-edge-case.lzma",
+        "tests/files/range-coder-edge-case",
+    );
 }
 
 #[test]