Infinite loop inside white block due to improper implementation of retrace detection.

[your-diary]

The spec says (emphasis mine)

Each time the interpreter hits a restriction while within the white block, it toggles the CC and steps the DP clockwise, then tries to slide again. This process repeats until the interpreter either enters a coloured block (where execution then continues); or until the interpreter begins retracing its route. If it retraces its route entirely within a white block, there is no way out of the white block and execution should terminate.

However, it seems this is not properly implemented.

How to Reproduce

1. Download this small image

   

2. Run cargo run -- <downloaded_image> --verbose

Expected Trace

Actual Trace

(0, 0)
(1, 5)
(1, 6)
(1, 7)
(1, 8)
(2, 8)
(3, 8)
(3, 7)
(3, 6)
(2, 6)
(1, 6)
(1, 7)
(1, 8)
(2, 8)
...

[your-diary]

I've already identified the cause and will fix it in days.

[your-diary]

Fixed locally. Will be pushed and released in a few days.

(0, 0)       DP:Right CC:Left
(1, 5)       DP:Right CC:Left
(1, 6)       DP:Right CC:Left
(1, 7)       DP:Right CC:Left
(1, 8)       DP:Right CC:Left
(1, 8)       DP:Down  CC:Right
(2, 8)       DP:Down  CC:Right
(3, 8)       DP:Down  CC:Right
(3, 8)       DP:Left  CC:Left
(3, 7)       DP:Left  CC:Left
(3, 6)       DP:Left  CC:Left
(3, 6)       DP:Up    CC:Right
(2, 6)       DP:Up    CC:Right
(1, 6)       DP:Up    CC:Right
(1, 6)       DP:Right CC:Left