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diff: remove redundant hash map lookup of uncommon shared words

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This commit is contained in:
Yuya Nishihara 2024-09-27 11:54:02 +09:00
parent 5c52b4ec13
commit 64e1ae277d
1 changed files with 23 additions and 31 deletions
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54
lib/src/diff.rs
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@ -122,12 +122,13 @@ impl<'input> Histogram<'input> {
Histogram { word_to_positions }
}
fn build_count_to_words(&self) -> BTreeMap<usize, Vec<&'input BStr>> {
let mut count_to_words: BTreeMap<usize, Vec<&BStr>> = BTreeMap::new();
for (word, ranges) in &self.word_to_positions {
count_to_words.entry(ranges.len()).or_default().push(word);
fn build_count_to_entries(&self) -> BTreeMap<usize, Vec<(&'input BStr, &Vec<WordPosition>)>> {
let mut count_to_entries: BTreeMap<usize, Vec<_>> = BTreeMap::new();
for (word, positions) in &self.word_to_positions {
let entries = count_to_entries.entry(positions.len()).or_default();
entries.push((*word, positions));
}
count_to_words
count_to_entries
}
}
@ -233,8 +234,8 @@ fn unchanged_ranges_lcs(
) -> Vec<(Range<usize>, Range<usize>)> {
let max_occurrences = 100;
let left_histogram = Histogram::calculate(left, max_occurrences);
let left_count_to_words = left_histogram.build_count_to_words();
if *left_count_to_words.keys().next().unwrap() > max_occurrences {
let left_count_to_entries = left_histogram.build_count_to_entries();
if *left_count_to_entries.keys().next().unwrap() > max_occurrences {
// If there are very many occurrences of all words, then we just give up.
return vec![];
}
@ -242,38 +243,29 @@ fn unchanged_ranges_lcs(
// Look for words with few occurrences in `left` (could equally well have picked
// `right`?). If any of them also occur in `right`, then we add the words to
// the LCS.
let Some(uncommon_shared_words) = left_count_to_words
.iter()
.map(|(left_count, left_words)| -> Vec<&BStr> {
left_words
let Some(uncommon_shared_word_positions) =
left_count_to_entries.values().find_map(|left_entries| {
let mut both_positions = left_entries
.iter()
.copied()
.filter(|left_word| {
let right_count = right_histogram
.word_to_positions
.get(left_word)
.map_or(0, |right_positions| right_positions.len());
*left_count == right_count
.filter_map(|&(word, left_positions)| {
let right_positions = right_histogram.word_to_positions.get(word)?;
(left_positions.len() == right_positions.len())
.then_some((left_positions, right_positions))
})
.collect()
.peekable();
both_positions.peek().is_some().then_some(both_positions)
})
.find(|words| !words.is_empty())
else {
return vec![];
};
// [(index into ranges, serial to identify {word, occurrence #})]
let (mut left_positions, mut right_positions): (Vec<_>, Vec<_>) = uncommon_shared_words
.iter()
.flat_map(|word| {
let left_occurrences = &left_histogram.word_to_positions[word];
let right_occurrences = &right_histogram.word_to_positions[word];
assert_eq!(left_occurrences.len(), right_occurrences.len());
iter::zip(left_occurrences, right_occurrences)
})
.enumerate()
.map(|(serial, (&left_pos, &right_pos))| ((left_pos, serial), (right_pos, serial)))
.unzip();
let (mut left_positions, mut right_positions): (Vec<_>, Vec<_>) =
uncommon_shared_word_positions
.flat_map(|(lefts, rights)| iter::zip(lefts, rights))
.enumerate()
.map(|(serial, (&left_pos, &right_pos))| ((left_pos, serial), (right_pos, serial)))
.unzip();
left_positions.sort_unstable_by_key(|&(pos, _serial)| pos);
right_positions.sort_unstable_by_key(|&(pos, _serial)| pos);
let left_index_by_right_index: Vec<usize> = {