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// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
use crate::interval_set::{Interval, IntervalBound};
use alloc::collections::vec_deque::{self, VecDeque};
use core::cmp::Ordering;
/// An iterator of `Intervals` over the intersection of two sets,
/// i.e. the values in both `A` and `B` will be returned.
#[derive(Debug)]
pub struct Intersection<'a, T> {
set_a: vec_deque::Iter<'a, Interval<T>>,
set_b: vec_deque::Iter<'a, Interval<T>>,
interval_a: Option<Interval<T>>,
interval_b: Option<Interval<T>>,
}
impl<'a, T: Copy> Intersection<'a, T> {
pub(crate) fn new(set_a: &'a VecDeque<Interval<T>>, set_b: &'a VecDeque<Interval<T>>) -> Self {
let mut set_a = set_a.iter();
let interval_a = set_a.next().cloned();
let mut set_b = set_b.iter();
let interval_b = set_b.next().cloned();
Self {
set_a,
set_b,
interval_a,
interval_b,
}
}
}
impl<'a, T: 'a + IntervalBound + Ord> Iterator for Intersection<'a, T> {
type Item = Interval<T>;
fn next(&mut self) -> Option<Self::Item> {
use Ordering::*;
let interval_a = self.interval_a.as_mut()?;
let interval_b = self.interval_b.as_mut()?;
macro_rules! advance_set_a {
() => {
self.interval_a = self.set_a.next().cloned();
};
}
macro_rules! advance_set_b {
() => {
self.interval_b = self.set_b.next().cloned();
};
}
loop {
match (
interval_a.start.cmp(&interval_b.start),
interval_a.end.cmp(&interval_b.end),
) {
// interval A is a subset of interval B
//
// interval A: |-----|
// interval B: |---------|
//
// Returns:
// |-----|
//
(Equal, Less) |
// interval A is a subset of interval B
//
// interval A: |----|
// interval B: |---------|
//
// Returns:
// |----|
//
(Greater, Less) => {
let item = *interval_a;
interval_b.start = interval_a.end_exclusive();
advance_set_a!();
return Some(item);
}
// interval A contains interval B, spilling over into the next slot
//
// interval A: |---------|
// interval B: |---|
//
// Returns:
// |---|
//
(Equal, Greater) |
// interval A contains interval B, spilling over into the next slot
//
// interval A: |---------|
// interval B: |---|
//
// Returns:
// |---|
//
(Less, Greater) => {
let item = *interval_b;
interval_a.start = interval_b.end_exclusive();
advance_set_b!();
return Some(item);
}
// interval A is a subset of interval B
//
// interval A: |-----|
// interval B: |---------|
//
// Returns:
// |-----|
//
(Greater, Equal) |
// the intervals are equal
//
// interval A: |---------|
// interval B: |---------|
//
// Returns:
// |---------|
//
(Equal, Equal) => {
let item = *interval_a;
advance_set_a!();
advance_set_b!();
return Some(item);
}
// interval A ends with interval B
//
// interval A: |---------|
// interval B: |---|
//
// Returns:
// |---|
//
(Less, Equal) => {
let item = *interval_b;
advance_set_a!();
advance_set_b!();
return Some(item);
}
// interval A is part of interval B.
//
// interval A: |--------|
// interval B: |--------|
//
// Returns:
// |---|
//
(Greater, Greater) if interval_a.start <= interval_b.end => {
let mut item = *interval_a;
item.end = interval_b.end;
interval_a.start = item.end_exclusive();
advance_set_b!();
return Some(item);
}
// interval A overlaps part of interval B
//
// interval A: |--------|
// interval B: |--------|
//
// Returns:
// |---|
//
(Less, Less) if interval_a.end >= interval_b.start => {
let mut item = *interval_b;
item.end = interval_a.end;
interval_b.start = item.end_exclusive();
advance_set_a!();
return Some(item);
}
// interval A comes later
//
// interval A: |-----|
// interval B: |----|
//
// continue to next B
//
(Greater, Greater) => {
*interval_b = self.set_b.next().cloned()?;
continue;
}
// interval A comes before interval B
//
// interval A: |---|
// interval B: |--------|
//
// continue to next A
//
(Less, Less) => {
*interval_a = self.set_a.next().cloned()?;
continue;
}
}
}
}
}
/// Apply the intersection of `set_a` with `set_b` to `set_a`
#[inline]
pub(super) fn apply<T: IntervalBound>(
set_a: &mut VecDeque<Interval<T>>,
set_b: &VecDeque<Interval<T>>,
) {
use Ordering::*;
if set_a.is_empty() {
return;
}
if set_b.is_empty() {
set_a.clear();
return;
}
let mut set_b = set_b.iter();
let mut interval_b = set_b.next().expect("set_b is not empty");
let mut a_index = 0;
macro_rules! advance_set_a {
() => {
a_index += 1;
};
}
macro_rules! advance_set_b {
() => {
if let Some(next_interval_b) = set_b.next() {
interval_b = next_interval_b;
} else {
// the remainder of set_a is not in the intersection, since we've
// reached the end of set_b
set_a.truncate(a_index);
return;
}
};
}
// Inserts a new interval into the next index of set_a that starts where the current interval b
// ends (with a gap of 1) and ends where the current interval a ends
macro_rules! split_off_a {
($interval_a:ident) => {
// step_up_saturating is used because the next intersecting interval should not be
// contiguous with the current interval, so we can expect a gap of at least 1.
let new_interval_a: Interval<T> =
(interval_b.end_exclusive().step_up_saturating()..=$interval_a.end).into();
if new_interval_a.is_valid() {
// if interval_a had only overlapped interval_b by 1, then the new interval
// will not be valid and we can skip inserting it
// for example: interval_a = [0..=48], interval_b = [0..=47]
// new_interval_a = [49..=48] since we know 48 is not in interval_b
set_a.insert(a_index + 1, new_interval_a);
}
};
}
while let Some(interval_a) = set_a.get(a_index) {
match (interval_a.start.cmp(&interval_b.start),
interval_a.end.cmp(&interval_b.end),
) {
// interval A is a subset of interval B
//
// interval A: |-----|
// interval B: |---------|
//
// End state:
// |-----|
// a_index: ^
(Equal, Less) |
// interval A is a subset of interval B
//
// interval A: |----|
// interval B: |---------|
//
// End state:
// |----|
// a_index: ^
(Greater, Less) => {
advance_set_a!();
}
// interval A contains interval B, spilling over into the next slot
//
// interval A: |---------|
// interval B: |---|
//
// End state:
// |---| |---|
// a_index: ^
(Equal, Greater) |
// interval A contains interval B, spilling over into the next slot
//
// interval A: |---------|
// interval B: |---|
//
// End state:
// |---| |-|
// a_index: ^
(Less, Greater) => {
// split off the part of interval A that is spilling into the next slot
split_off_a!(interval_a);
set_a[a_index] = *interval_b;
advance_set_a!();
advance_set_b!();
}
// interval A is a subset of interval B
//
// interval A: |-----|
// interval B: |---------|
//
// End state:
// |-----|
// a_index: ^
(Greater, Equal) |
// the intervals are equal
//
// interval A: |---------|
// interval B: |---------|
//
// End state:
// |---------|
// a_index: ^
(Equal, Equal) => {
advance_set_a!();
advance_set_b!();
}
// interval A ends with interval B
//
// interval A: |---------|
// interval B: |---|
//
// End state:
// |---|
// a_index: ^
(Less, Equal) => {
set_a[a_index].start = interval_b.start;
advance_set_a!();
advance_set_b!();
}
// interval A overlaps part of interval B.
//
// interval A: |--------|
// interval B: |--------|
//
// End state:
// |---| |--|
// a_index: ^
(Greater, Greater) if interval_a.start <= interval_b.end => {
// split off the part of interval A that is spilling into the next slot
split_off_a!(interval_a);
set_a[a_index].end = interval_b.end;
advance_set_a!();
advance_set_b!();
}
// interval A overlaps part of interval B
//
// interval A: |--------|
// interval B: |--------|
//
// End state:
// |---|
// a_index: ^
(Less, Less) if interval_a.end >= interval_b.start => {
set_a[a_index].start = interval_b.start;
advance_set_a!();
}
// interval A comes later
//
// interval A: |-----|
// interval B: |----|
//
// continue to next B
//
(Greater, Greater) => {
advance_set_b!();
}
// interval A comes before interval B
//
// interval A: |---|
// interval B: |--------|
//
// remove A and continue to next A
//
(Less, Less) => {
set_a.remove(a_index);
}
}
}
}