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use std::collections::{HashMap, HashSet};
use std::hash::Hash;
use visit::{DfsPostOrder, GraphBase, IntoNeighbors, Visitable, Walker};
#[derive(Debug, Clone)]
pub struct Dominators<N>
where N: Copy + Eq + Hash
{
root: N,
dominators: HashMap<N, N>,
}
impl<N> Dominators<N>
where N: Copy + Eq + Hash
{
pub fn root(&self) -> N {
self.root
}
pub fn immediate_dominator(&self, node: N) -> Option<N> {
if node == self.root {
None
} else {
self.dominators.get(&node).cloned()
}
}
pub fn strict_dominators(&self, node: N) -> Option<DominatorsIter<N>> {
if self.dominators.contains_key(&node) {
Some(DominatorsIter {
dominators: self,
node: self.immediate_dominator(node),
})
} else {
None
}
}
pub fn dominators(&self, node: N) -> Option<DominatorsIter<N>> {
if self.dominators.contains_key(&node) {
Some(DominatorsIter {
dominators: self,
node: Some(node),
})
} else {
None
}
}
}
pub struct DominatorsIter<'a, N>
where N: 'a + Copy + Eq + Hash
{
dominators: &'a Dominators<N>,
node: Option<N>,
}
impl<'a, N> Iterator for DominatorsIter<'a, N>
where N: 'a + Copy + Eq + Hash
{
type Item = N;
fn next(&mut self) -> Option<Self::Item> {
let next = self.node.take();
if let Some(next) = next {
self.node = self.dominators.immediate_dominator(next);
}
next
}
}
const UNDEFINED: usize = ::std::usize::MAX;
pub fn simple_fast<G>(graph: G, root: G::NodeId) -> Dominators<G::NodeId>
where G: IntoNeighbors + Visitable,
<G as GraphBase>::NodeId: Eq + Hash
{
let (post_order, predecessor_sets) = simple_fast_post_order(graph, root);
let length = post_order.len();
debug_assert!(length > 0);
debug_assert!(post_order.last() == Some(&root));
let node_to_post_order_idx: HashMap<_, _> = post_order.iter()
.enumerate()
.map(|(idx, &node)| (node, idx))
.collect();
let idx_to_predecessor_vec =
predecessor_sets_to_idx_vecs(&post_order, &node_to_post_order_idx, predecessor_sets);
let mut dominators = vec![UNDEFINED; length];
dominators[length - 1] = length - 1;
let mut changed = true;
while changed {
changed = false;
for idx in (0..length - 1).rev() {
debug_assert!(post_order[idx] != root);
let new_idom_idx = {
let mut predecessors =
idx_to_predecessor_vec[idx].iter().filter(|&&p| dominators[p] != UNDEFINED);
let new_idom_idx = predecessors.next()
.expect("Because the root is initialized to dominate itself, and is the \
first node in every path, there must exist a predecessor to this \
node that also has a dominator");
predecessors.fold(*new_idom_idx, |new_idom_idx, &predecessor_idx| {
intersect(&dominators, new_idom_idx, predecessor_idx)
})
};
debug_assert!(new_idom_idx < length);
if new_idom_idx != dominators[idx] {
dominators[idx] = new_idom_idx;
changed = true;
}
}
}
debug_assert!(!dominators.iter().any(|&dom| dom == UNDEFINED));
Dominators {
root: root,
dominators: dominators.into_iter()
.enumerate()
.map(|(idx, dom_idx)| (post_order[idx], post_order[dom_idx]))
.collect(),
}
}
fn intersect(dominators: &[usize], mut finger1: usize, mut finger2: usize) -> usize {
while finger1 != finger2 {
if finger1 < finger2 {
finger1 = dominators[finger1];
} else if finger2 < finger1 {
finger2 = dominators[finger2];
}
}
finger1
}
fn predecessor_sets_to_idx_vecs<N>(post_order: &[N],
node_to_post_order_idx: &HashMap<N, usize>,
mut predecessor_sets: HashMap<N, HashSet<N>>)
-> Vec<Vec<usize>>
where N: Copy + Eq + Hash
{
post_order.iter()
.map(|node| {
predecessor_sets.remove(node)
.map(|predecessors| {
predecessors.into_iter()
.map(|p| *node_to_post_order_idx.get(&p).unwrap())
.collect()
})
.unwrap_or(vec![])
})
.collect()
}
fn simple_fast_post_order<G>(graph: G,
root: G::NodeId)
-> (Vec<G::NodeId>, HashMap<G::NodeId, HashSet<G::NodeId>>)
where G: IntoNeighbors + Visitable,
<G as GraphBase>::NodeId: Eq + Hash
{
let mut post_order = vec![];
let mut predecessor_sets = HashMap::new();
for node in DfsPostOrder::new(graph, root).iter(graph) {
post_order.push(node);
for successor in graph.neighbors(node) {
predecessor_sets.entry(successor)
.or_insert_with(HashSet::new)
.insert(node);
}
}
(post_order, predecessor_sets)
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_iter_dominators() {
let doms: Dominators<u32> = Dominators {
root: 0,
dominators: [(2, 1), (1, 0), (0, 0)]
.iter()
.cloned()
.collect(),
};
let all_doms: Vec<_> = doms.dominators(2).unwrap().collect();
assert_eq!(vec![2, 1, 0], all_doms);
assert_eq!(None::<()>, doms.dominators(99).map(|_| unreachable!()));
let strict_doms: Vec<_> = doms.strict_dominators(2).unwrap().collect();
assert_eq!(vec![1, 0], strict_doms);
assert_eq!(None::<()>, doms.strict_dominators(99).map(|_| unreachable!()));
}
}