293 lines
8.9 KiB
Rust
293 lines
8.9 KiB
Rust
use collections::HashMap;
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use ordered_float::OrderedFloat;
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use std::{
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cmp,
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fmt::{self, Debug},
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ops::Range,
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};
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struct Matrix {
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cells: Vec<f64>,
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rows: usize,
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cols: usize,
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}
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impl Matrix {
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fn new() -> Self {
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Self {
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cells: Vec::new(),
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rows: 0,
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cols: 0,
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}
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}
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fn resize(&mut self, rows: usize, cols: usize) {
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self.cells.resize(rows * cols, 0.);
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self.rows = rows;
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self.cols = cols;
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}
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fn get(&self, row: usize, col: usize) -> f64 {
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if row >= self.rows {
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panic!("row out of bounds")
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}
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if col >= self.cols {
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panic!("col out of bounds")
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}
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self.cells[col * self.rows + row]
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}
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fn set(&mut self, row: usize, col: usize, value: f64) {
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if row >= self.rows {
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panic!("row out of bounds")
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}
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if col >= self.cols {
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panic!("col out of bounds")
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}
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self.cells[col * self.rows + row] = value;
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}
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}
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impl Debug for Matrix {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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writeln!(f)?;
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for i in 0..self.rows {
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for j in 0..self.cols {
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write!(f, "{:5}", self.get(i, j))?;
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}
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writeln!(f)?;
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}
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Ok(())
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}
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}
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#[derive(Debug)]
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pub enum Hunk {
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Insert { text: String },
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Remove { len: usize },
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Keep { len: usize },
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}
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pub struct StreamingDiff {
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old: Vec<char>,
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new: Vec<char>,
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scores: Matrix,
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old_text_ix: usize,
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new_text_ix: usize,
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equal_runs: HashMap<(usize, usize), u32>,
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}
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impl StreamingDiff {
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const INSERTION_SCORE: f64 = -1.;
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const DELETION_SCORE: f64 = -20.;
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const EQUALITY_BASE: f64 = 1.8;
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const MAX_EQUALITY_EXPONENT: i32 = 16;
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pub fn new(old: String) -> Self {
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let old = old.chars().collect::<Vec<_>>();
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let mut scores = Matrix::new();
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scores.resize(old.len() + 1, 1);
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for i in 0..=old.len() {
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scores.set(i, 0, i as f64 * Self::DELETION_SCORE);
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}
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Self {
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old,
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new: Vec::new(),
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scores,
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old_text_ix: 0,
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new_text_ix: 0,
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equal_runs: Default::default(),
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}
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}
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pub fn push_new(&mut self, text: &str) -> Vec<Hunk> {
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self.new.extend(text.chars());
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self.scores.resize(self.old.len() + 1, self.new.len() + 1);
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for j in self.new_text_ix + 1..=self.new.len() {
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self.scores.set(0, j, j as f64 * Self::INSERTION_SCORE);
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for i in 1..=self.old.len() {
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let insertion_score = self.scores.get(i, j - 1) + Self::INSERTION_SCORE;
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let deletion_score = self.scores.get(i - 1, j) + Self::DELETION_SCORE;
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let equality_score = if self.old[i - 1] == self.new[j - 1] {
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let mut equal_run = self.equal_runs.get(&(i - 1, j - 1)).copied().unwrap_or(0);
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equal_run += 1;
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self.equal_runs.insert((i, j), equal_run);
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let exponent = cmp::min(equal_run as i32 / 4, Self::MAX_EQUALITY_EXPONENT);
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self.scores.get(i - 1, j - 1) + Self::EQUALITY_BASE.powi(exponent)
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} else {
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f64::NEG_INFINITY
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};
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let score = insertion_score.max(deletion_score).max(equality_score);
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self.scores.set(i, j, score);
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}
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}
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let mut max_score = f64::NEG_INFINITY;
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let mut next_old_text_ix = self.old_text_ix;
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let next_new_text_ix = self.new.len();
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for i in self.old_text_ix..=self.old.len() {
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let score = self.scores.get(i, next_new_text_ix);
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if score > max_score {
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max_score = score;
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next_old_text_ix = i;
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}
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}
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let hunks = self.backtrack(next_old_text_ix, next_new_text_ix);
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self.old_text_ix = next_old_text_ix;
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self.new_text_ix = next_new_text_ix;
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hunks
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}
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fn backtrack(&self, old_text_ix: usize, new_text_ix: usize) -> Vec<Hunk> {
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let mut pending_insert: Option<Range<usize>> = None;
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let mut hunks = Vec::new();
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let mut i = old_text_ix;
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let mut j = new_text_ix;
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while (i, j) != (self.old_text_ix, self.new_text_ix) {
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let insertion_score = if j > self.new_text_ix {
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Some((i, j - 1))
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} else {
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None
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};
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let deletion_score = if i > self.old_text_ix {
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Some((i - 1, j))
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} else {
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None
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};
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let equality_score = if i > self.old_text_ix && j > self.new_text_ix {
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if self.old[i - 1] == self.new[j - 1] {
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Some((i - 1, j - 1))
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} else {
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None
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}
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} else {
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None
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};
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let (prev_i, prev_j) = [insertion_score, deletion_score, equality_score]
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.iter()
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.max_by_key(|cell| cell.map(|(i, j)| OrderedFloat(self.scores.get(i, j))))
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.unwrap()
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.unwrap();
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if prev_i == i && prev_j == j - 1 {
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if let Some(pending_insert) = pending_insert.as_mut() {
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pending_insert.start = prev_j;
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} else {
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pending_insert = Some(prev_j..j);
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}
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} else {
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if let Some(range) = pending_insert.take() {
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hunks.push(Hunk::Insert {
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text: self.new[range].iter().collect(),
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});
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}
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let char_len = self.old[i - 1].len_utf8();
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if prev_i == i - 1 && prev_j == j {
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if let Some(Hunk::Remove { len }) = hunks.last_mut() {
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*len += char_len;
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} else {
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hunks.push(Hunk::Remove { len: char_len })
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}
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} else {
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if let Some(Hunk::Keep { len }) = hunks.last_mut() {
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*len += char_len;
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} else {
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hunks.push(Hunk::Keep { len: char_len })
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}
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}
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}
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i = prev_i;
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j = prev_j;
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}
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if let Some(range) = pending_insert.take() {
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hunks.push(Hunk::Insert {
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text: self.new[range].iter().collect(),
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});
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}
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hunks.reverse();
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hunks
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}
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pub fn finish(self) -> Vec<Hunk> {
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self.backtrack(self.old.len(), self.new.len())
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}
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}
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#[cfg(test)]
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mod tests {
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use std::env;
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use super::*;
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use rand::prelude::*;
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#[gpui::test(iterations = 100)]
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fn test_random_diffs(mut rng: StdRng) {
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let old_text_len = env::var("OLD_TEXT_LEN")
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.map(|i| i.parse().expect("invalid `OLD_TEXT_LEN` variable"))
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.unwrap_or(10);
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let new_text_len = env::var("NEW_TEXT_LEN")
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.map(|i| i.parse().expect("invalid `NEW_TEXT_LEN` variable"))
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.unwrap_or(10);
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let old = util::RandomCharIter::new(&mut rng)
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.take(old_text_len)
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.collect::<String>();
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log::info!("old text: {:?}", old);
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let mut diff = StreamingDiff::new(old.clone());
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let mut hunks = Vec::new();
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let mut new_len = 0;
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let mut new = String::new();
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while new_len < new_text_len {
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let new_chunk_len = rng.gen_range(1..=new_text_len - new_len);
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let new_chunk = util::RandomCharIter::new(&mut rng)
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.take(new_len)
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.collect::<String>();
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log::info!("new chunk: {:?}", new_chunk);
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new_len += new_chunk_len;
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new.push_str(&new_chunk);
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let new_hunks = diff.push_new(&new_chunk);
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log::info!("hunks: {:?}", new_hunks);
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hunks.extend(new_hunks);
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}
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let final_hunks = diff.finish();
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log::info!("final hunks: {:?}", final_hunks);
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hunks.extend(final_hunks);
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log::info!("new text: {:?}", new);
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let mut old_ix = 0;
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let mut new_ix = 0;
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let mut patched = String::new();
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for hunk in hunks {
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match hunk {
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Hunk::Keep { len } => {
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assert_eq!(&old[old_ix..old_ix + len], &new[new_ix..new_ix + len]);
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patched.push_str(&old[old_ix..old_ix + len]);
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old_ix += len;
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new_ix += len;
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}
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Hunk::Remove { len } => {
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old_ix += len;
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}
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Hunk::Insert { text } => {
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assert_eq!(text, &new[new_ix..new_ix + text.len()]);
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patched.push_str(&text);
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new_ix += text.len();
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}
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}
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}
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assert_eq!(patched, new);
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}
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}
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