diff --git a/content/posts/2024-07-06-gap-buffer/index.md b/content/posts/2024-07-06-gap-buffer/index.md index 30b9c79..979cb71 100644 --- a/content/posts/2024-07-06-gap-buffer/index.md +++ b/content/posts/2024-07-06-gap-buffer/index.md @@ -158,3 +158,33 @@ def delete(self, dist: int = 1) -> None: # Extend gap to the right self._gap_end += dist ``` + +### Moving the cursor + +Moving the cursor along the buffer will shift letters from one side of the gap +to the other, moving them accross from prefix to suffix and back. + +I find Python's list slicing not quite as elegant to read as a `memmove`, though +it does make for a very small and efficient implementation. + +```python +def left(self, dist: int = 1) -> None: + assert dist <= self.prefix_length + # Shift the needed number of characters from end of prefix to start of suffix + self._buf[self._gap_end - dist : self._gap_end] = self._buf[ + self._gap_start - dist : self._gap_start + ] + # Adjust indices accordingly + self._gap_start -= dist + self._gap_end -= dist + +def right(self, dist: int = 1) -> None: + assert dist <= self.suffix_length + # Shift the needed number of characters from start of suffix to end of prefix + self._buf[self._gap_start : self._gap_start + dist] = self._buf[ + self._gap_end : self._gap_end + dist + ] + # Adjust indices accordingly + self._gap_start += dist + self._gap_end += dist +```