This is a C++ implementation of Langton's ant with RLR rules. It runs a given number of steps as quickly as possible and then saves a PNG (and optionally a checkpoint) of the result. On a Ryzen 9 7950X with Arch Linux, it runs at about 250 million steps per second and takes about 70 minutes to do one trillion steps. I've computed 20 trillion steps so far and there's still no highway.
This uses an expandable 2D grid. When the ant reaches an edge of the grid, a new grid is created with 4x the area of the old grid and the old grid is moved to the center of the new grid.
./langton: 1000 steps, no checkpoint./langton 1000000000: one billion steps, no checkpoint./langton 1000000000000 langton.zst: one trillion steps, checkpoint stored inlangton.zst