Incorrect decompresion

[jrmuizel]

The attached file does not decompress properly with libzbitmap.

Apple's decompressor decodes it to a file with md5: 466028bba5a7d61369e23302cfe87282
libzbitmap decodes to a file with md5: 628ccd8a5ebf3e8b285f73e36fac42c8

dp_bug_repro.zip

[jrmuizel]

Note. The compressed file was made with my own compressor so it may be incorrectly encoded.

[eafer]

Thanks for the report. Crazy that you found a bug after so many years. Can you send me the uncompressed file? Also is your compressor public?

[jrmuizel]

This is the original file and what libzbitmap decodes to. I've also included the output from the Apple decompressor.
dp_bug_repro-decomp.zip

[jrmuizel]

It looks like the output of Apple decompressor depends on the contents of the output buffer.

[eafer]

It seems that repetition periods can only be 8 bytes or more, so the bug is in your compressor (and mine). Apple accepts shorter periods but then it reads uninitialized data from the output buffer.

[eafer]

My decompressor doesn't have this problem because we work one byte at a time, Apple's implementation is far more fancy.

[eafer]

It seems that I was actually aware of this at the time, and my compressor doesn't produce periods under 8 bytes. For some reason I did allow it in the decompressor, I guess it might be better to just throw an error.

I could also aim for identical behaviour with the Apple implementation and intentionally read uninitialized memory...

[jrmuizel]

My compressor isn't public yet.