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graphemes: Optimize nth_next/nth_prev operation.

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It's used a lot more than it used to in position calculation. Instead of
throwing away state between boundary calculation, reuse it.
This commit is contained in:
Blaž Hrastnik 2021-02-24 17:12:44 +09:00
parent f118e7580f
commit 6bd16a7320
1 changed files with 55 additions and 61 deletions
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56
helix-core/src/graphemes.rs
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@ -27,23 +27,11 @@ pub fn grapheme_width(g: &str) -> usize {
}
pub fn nth_prev_grapheme_boundary(slice: RopeSlice, char_idx: usize, n: usize) -> usize {
// TODO: implement this more efficiently. This has to do a lot of
// re-scanning of rope chunks. Probably move the main implementation here,
// and have prev_grapheme_boundary call this instead.
let mut char_idx = char_idx;
for _ in 0..n {
char_idx = prev_grapheme_boundary(slice, char_idx);
}
char_idx
}
/// Finds the previous grapheme boundary before the given char position.
pub fn prev_grapheme_boundary(slice: RopeSlice, char_idx: usize) -> usize {
// Bounds check
debug_assert!(char_idx <= slice.len_chars());
// We work with bytes for this, so convert.
let byte_idx = slice.char_to_byte(char_idx);
let mut byte_idx = slice.char_to_byte(char_idx);
// Get the chunk with our byte index in it.
let (mut chunk, mut chunk_byte_idx, mut chunk_char_idx, _) = slice.chunk_at_byte(byte_idx);
@ -52,12 +40,13 @@ pub fn prev_grapheme_boundary(slice: RopeSlice, char_idx: usize) -> usize {
let mut gc = GraphemeCursor::new(byte_idx, slice.len_bytes(), true);
// Find the previous grapheme cluster boundary.
for _ in 0..n {
loop {
match gc.prev_boundary(chunk, chunk_byte_idx) {
Ok(None) => return 0,
Ok(Some(n)) => {
let tmp = byte_to_char_idx(chunk, n - chunk_byte_idx);
return chunk_char_idx + tmp;
byte_idx = n;
break;
}
Err(GraphemeIncomplete::PrevChunk) => {
let (a, b, c, _) = slice.chunk_at_byte(chunk_byte_idx - 1);
@ -73,25 +62,21 @@ pub fn prev_grapheme_boundary(slice: RopeSlice, char_idx: usize) -> usize {
}
}
}
let tmp = byte_to_char_idx(chunk, byte_idx + chunk_byte_idx);
chunk_char_idx + tmp
}
/// Finds the previous grapheme boundary before the given char position.
pub fn prev_grapheme_boundary(slice: RopeSlice, char_idx: usize) -> usize {
nth_prev_grapheme_boundary(slice, char_idx, 1)
}
pub fn nth_next_grapheme_boundary(slice: RopeSlice, char_idx: usize, n: usize) -> usize {
// TODO: implement this more efficiently. This has to do a lot of
// re-scanning of rope chunks. Probably move the main implementation here,
// and have next_grapheme_boundary call this instead.
let mut char_idx = char_idx;
for _ in 0..n {
char_idx = next_grapheme_boundary(slice, char_idx);
}
char_idx
}
/// Finds the next grapheme boundary after the given char position.
pub fn next_grapheme_boundary(slice: RopeSlice, char_idx: usize) -> usize {
// Bounds check
debug_assert!(char_idx <= slice.len_chars());
// We work with bytes for this, so convert.
let byte_idx = slice.char_to_byte(char_idx);
let mut byte_idx = slice.char_to_byte(char_idx);
// Get the chunk with our byte index in it.
let (mut chunk, mut chunk_byte_idx, mut chunk_char_idx, _) = slice.chunk_at_byte(byte_idx);
@ -99,13 +84,14 @@ pub fn next_grapheme_boundary(slice: RopeSlice, char_idx: usize) -> usize {
// Set up the grapheme cursor.
let mut gc = GraphemeCursor::new(byte_idx, slice.len_bytes(), true);
// Find the next grapheme cluster boundary.
// Find the nth next grapheme cluster boundary.
for _ in 0..n {
loop {
match gc.next_boundary(chunk, chunk_byte_idx) {
Ok(None) => return slice.len_chars(),
Ok(Some(n)) => {
let tmp = byte_to_char_idx(chunk, n - chunk_byte_idx);
return chunk_char_idx + tmp;
byte_idx = n;
break;
}
Err(GraphemeIncomplete::NextChunk) => {
chunk_byte_idx += chunk.len();
@ -121,6 +107,14 @@ pub fn next_grapheme_boundary(slice: RopeSlice, char_idx: usize) -> usize {
}
}
}
let tmp = byte_to_char_idx(chunk, byte_idx - chunk_byte_idx);
chunk_char_idx + tmp
}
/// Finds the next grapheme boundary after the given char position.
pub fn next_grapheme_boundary(slice: RopeSlice, char_idx: usize) -> usize {
nth_next_grapheme_boundary(slice, char_idx, 1)
}
/// Returns whether the given char position is a grapheme boundary.
pub fn is_grapheme_boundary(slice: RopeSlice, char_idx: usize) -> bool {