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//! Hunt–McIlroy / Hunt–Szymanski LCS diff algorithm.
//!
//! * time: `O((NM)D log (M)D)`
//! * space `O(MN)`
use std::collections::BTreeMap;
use std::ops::{Index, Range};
use std::time::Instant;
use crate::algorithms::utils::{common_prefix_len, common_suffix_len, is_empty_range};
use crate::algorithms::DiffHook;
/// Hunt–McIlroy / Hunt–Szymanski LCS diff algorithm.
///
/// Diff `old`, between indices `old_range` and `new` between indices `new_range`.
///
/// This diff is done with an optional deadline that defines the maximal
/// execution time permitted before it bails and falls back to an very bad
/// approximation. Deadlines with LCS do not make a lot of sense and should
/// not be used.
pub fn diff<Old, New, D>(
d: &mut D,
old: &Old,
old_range: Range<usize>,
new: &New,
new_range: Range<usize>,
) -> Result<(), D::Error>
where
Old: Index<usize> + ?Sized,
New: Index<usize> + ?Sized,
D: DiffHook,
New::Output: PartialEq<Old::Output>,
{
diff_deadline(d, old, old_range, new, new_range, None)
}
/// Hunt–McIlroy / Hunt–Szymanski LCS diff algorithm.
///
/// Diff `old`, between indices `old_range` and `new` between indices `new_range`.
///
/// This diff is done with an optional deadline that defines the maximal
/// execution time permitted before it bails and falls back to an approximation.
pub fn diff_deadline<Old, New, D>(
d: &mut D,
old: &Old,
old_range: Range<usize>,
new: &New,
new_range: Range<usize>,
deadline: Option<Instant>,
) -> Result<(), D::Error>
where
Old: Index<usize> + ?Sized,
New: Index<usize> + ?Sized,
D: DiffHook,
New::Output: PartialEq<Old::Output>,
{
if is_empty_range(&new_range) {
d.delete(old_range.start, old_range.len(), new_range.start)?;
return Ok(());
} else if is_empty_range(&old_range) {
d.insert(old_range.start, new_range.start, new_range.len())?;
return Ok(());
}
let common_prefix_len = common_prefix_len(old, old_range.clone(), new, new_range.clone());
let common_suffix_len = common_suffix_len(old, old_range.clone(), new, new_range.clone());
let maybe_table = make_table(
old,
common_prefix_len..(old_range.len() - common_suffix_len),
new,
common_prefix_len..(new_range.len() - common_suffix_len),
deadline,
);
let mut old_idx = 0;
let mut new_idx = 0;
let new_len = new_range.len() - common_prefix_len - common_suffix_len;
let old_len = old_range.len() - common_prefix_len - common_suffix_len;
if common_prefix_len > 0 {
d.equal(old_range.start, new_range.start, common_prefix_len)?;
}
if let Some(table) = maybe_table {
while new_idx < new_len && old_idx < old_len {
let old_orig_idx = old_range.start + common_prefix_len + old_idx;
let new_orig_idx = new_range.start + common_prefix_len + new_idx;
if new[new_orig_idx] == old[old_orig_idx] {
d.equal(old_orig_idx, new_orig_idx, 1)?;
old_idx += 1;
new_idx += 1;
} else if table.get(&(new_idx, old_idx + 1)).map_or(0, |&x| x)
>= table.get(&(new_idx + 1, old_idx)).map_or(0, |&x| x)
{
d.delete(old_orig_idx, 1, new_orig_idx)?;
old_idx += 1;
} else {
d.insert(old_orig_idx, new_orig_idx, 1)?;
new_idx += 1;
}
}
} else {
let old_orig_idx = old_range.start + common_prefix_len + old_idx;
let new_orig_idx = new_range.start + common_prefix_len + new_idx;
d.delete(old_orig_idx, old_len, new_orig_idx)?;
d.insert(old_orig_idx, new_orig_idx, new_len)?;
}
if old_idx < old_len {
d.delete(
old_range.start + common_prefix_len + old_idx,
old_len - old_idx,
new_range.start + common_prefix_len + new_idx,
)?;
old_idx += old_len - old_idx;
}
if new_idx < new_len {
d.insert(
old_range.start + common_prefix_len + old_idx,
new_range.start + common_prefix_len + new_idx,
new_len - new_idx,
)?;
}
if common_suffix_len > 0 {
d.equal(
old_range.start + old_len + common_prefix_len,
new_range.start + new_len + common_prefix_len,
common_suffix_len,
)?;
}
d.finish()
}
fn make_table<Old, New>(
old: &Old,
old_range: Range<usize>,
new: &New,
new_range: Range<usize>,
deadline: Option<Instant>,
) -> Option<BTreeMap<(usize, usize), u32>>
where
Old: Index<usize> + ?Sized,
New: Index<usize> + ?Sized,
New::Output: PartialEq<Old::Output>,
{
let old_len = old_range.len();
let new_len = new_range.len();
let mut table = BTreeMap::new();
for i in (0..new_len).rev() {
// are we running for too long? give up on the table
if let Some(deadline) = deadline {
if Instant::now() > deadline {
return None;
}
}
for j in (0..old_len).rev() {
let val = if new[i] == old[j] {
table.get(&(i + 1, j + 1)).map_or(0, |&x| x) + 1
} else {
table
.get(&(i + 1, j))
.map_or(0, |&x| x)
.max(table.get(&(i, j + 1)).map_or(0, |&x| x))
};
if val > 0 {
table.insert((i, j), val);
}
}
}
Some(table)
}
#[test]
fn test_table() {
let table = make_table(&vec![2, 3], 0..2, &vec![0, 1, 2], 0..3, None).unwrap();
let expected = {
let mut m = BTreeMap::new();
m.insert((1, 0), 1);
m.insert((0, 0), 1);
m.insert((2, 0), 1);
m
};
assert_eq!(table, expected);
}
#[test]
fn test_diff() {
let a: &[usize] = &[0, 1, 2, 3, 4];
let b: &[usize] = &[0, 1, 2, 9, 4];
let mut d = crate::algorithms::Replace::new(crate::algorithms::Capture::new());
diff(&mut d, a, 0..a.len(), b, 0..b.len()).unwrap();
insta::assert_debug_snapshot!(d.into_inner().ops());
}
#[test]
fn test_contiguous() {
let a: &[usize] = &[0, 1, 2, 3, 4, 4, 4, 5];
let b: &[usize] = &[0, 1, 2, 8, 9, 4, 4, 7];
let mut d = crate::algorithms::Replace::new(crate::algorithms::Capture::new());
diff(&mut d, a, 0..a.len(), b, 0..b.len()).unwrap();
insta::assert_debug_snapshot!(d.into_inner().ops());
}
#[test]
fn test_pat() {
let a: &[usize] = &[0, 1, 3, 4, 5];
let b: &[usize] = &[0, 1, 4, 5, 8, 9];
let mut d = crate::algorithms::Capture::new();
diff(&mut d, a, 0..a.len(), b, 0..b.len()).unwrap();
insta::assert_debug_snapshot!(d.ops());
}
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