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authorTavian Barnes <tavianator@tavianator.com>2020-05-09 16:34:54 -0400
committerTavian Barnes <tavianator@tavianator.com>2020-05-09 16:58:41 -0400
commit825515439247853af3714d3135051a83bd84d2e0 (patch)
treee9dcb7914a83114f9885abce6deb883048c4e551 /src/metric
parentcccde01c4b4e376e0d1b5f58bdc9b1fe70a9b930 (diff)
downloadkd-forest-825515439247853af3714d3135051a83bd84d2e0.tar.xz
metric/forest: Use a flat staging buffer to reduce tree building overhead
Diffstat (limited to 'src/metric')
-rw-r--r--src/metric/forest.rs86
1 files changed, 48 insertions, 38 deletions
diff --git a/src/metric/forest.rs b/src/metric/forest.rs
index 29b6f55..47eb413 100644
--- a/src/metric/forest.rs
+++ b/src/metric/forest.rs
@@ -4,14 +4,24 @@ use super::kd::KdTree;
use super::vp::VpTree;
use super::{Metric, NearestNeighbors, Neighborhood};
-use std::iter::{self, Extend, Flatten, FromIterator};
+use std::iter::{self, Extend, FromIterator};
+
+/// The number of bits dedicated to the flat buffer.
+const BUFFER_BITS: usize = 6;
+/// The maximum size of the buffer.
+const BUFFER_SIZE: usize = 1 << BUFFER_BITS;
/// A dynamic wrapper for a static nearest neighbor search data structure.
///
/// This type applies [dynamization](https://en.wikipedia.org/wiki/Dynamization) to an arbitrary
/// nearest neighbor search structure `T`, allowing new items to be added dynamically.
#[derive(Debug)]
-pub struct Forest<T>(Vec<Option<T>>);
+pub struct Forest<T: IntoIterator> {
+ /// A flat buffer used for the first few items, to avoid repeatedly rebuilding small trees.
+ buffer: Vec<T::Item>,
+ /// The trees of the forest, with sizes in geometric progression.
+ trees: Vec<Option<T>>,
+}
impl<T, U> Forest<U>
where
@@ -19,7 +29,10 @@ where
{
/// Create a new empty forest.
pub fn new() -> Self {
- Self(Vec::new())
+ Self {
+ buffer: Vec::new(),
+ trees: Vec::new(),
+ }
}
/// Add a new item to the forest.
@@ -29,10 +42,10 @@ where
/// Get the number of items in the forest.
pub fn len(&self) -> usize {
- let mut len = 0;
- for (i, slot) in self.0.iter().enumerate() {
+ let mut len = self.buffer.len();
+ for (i, slot) in self.trees.iter().enumerate() {
if slot.is_some() {
- len |= 1 << i;
+ len += 1 << (i + BUFFER_BITS);
}
}
len
@@ -44,32 +57,36 @@ where
U: FromIterator<T> + IntoIterator<Item = T>,
{
fn extend<I: IntoIterator<Item = T>>(&mut self, items: I) {
- let mut vec: Vec<_> = items.into_iter().collect();
- let new_len = self.len() + vec.len();
+ self.buffer.extend(items);
+ if self.buffer.len() < BUFFER_SIZE {
+ return;
+ }
+
+ let len = self.len();
for i in 0.. {
- let bit = 1 << i;
+ let bit = 1 << (i + BUFFER_BITS);
- if bit > new_len {
+ if bit > len {
break;
}
- if i >= self.0.len() {
- self.0.push(None);
+ if i >= self.trees.len() {
+ self.trees.push(None);
}
- if new_len & bit == 0 {
- if let Some(tree) = self.0[i].take() {
- vec.extend(tree);
+ if len & bit == 0 {
+ if let Some(tree) = self.trees[i].take() {
+ self.buffer.extend(tree);
}
- } else if self.0[i].is_none() {
- let offset = vec.len() - bit;
- self.0[i] = Some(vec.drain(offset..).collect());
+ } else if self.trees[i].is_none() {
+ let offset = self.buffer.len() - bit;
+ self.trees[i] = Some(self.buffer.drain(offset..).collect());
}
}
- debug_assert!(vec.is_empty());
- debug_assert!(self.len() == new_len);
+ debug_assert!(self.buffer.len() < BUFFER_SIZE);
+ debug_assert!(self.len() == len);
}
}
@@ -84,25 +101,13 @@ where
}
}
-type IntoIterImpl<T> = Flatten<Flatten<std::vec::IntoIter<Option<T>>>>;
-
-/// An iterator that moves items out of a forest.
-pub struct IntoIter<T: IntoIterator>(IntoIterImpl<T>);
-
-impl<T: IntoIterator> Iterator for IntoIter<T> {
- type Item = T::Item;
-
- fn next(&mut self) -> Option<Self::Item> {
- self.0.next()
- }
-}
-
impl<T: IntoIterator> IntoIterator for Forest<T> {
type Item = T::Item;
- type IntoIter = IntoIter<T>;
+ type IntoIter = std::vec::IntoIter<T::Item>;
- fn into_iter(self) -> Self::IntoIter {
- IntoIter(self.0.into_iter().flatten().flatten())
+ fn into_iter(mut self) -> Self::IntoIter {
+ self.buffer.extend(self.trees.into_iter().flatten().flatten());
+ self.buffer.into_iter()
}
}
@@ -110,14 +115,19 @@ impl<T, U, V> NearestNeighbors<T, U> for Forest<V>
where
U: Metric<T>,
V: NearestNeighbors<T, U>,
+ V: IntoIterator<Item = T>,
{
- fn search<'a, 'b, N>(&'a self, neighborhood: N) -> N
+ fn search<'a, 'b, N>(&'a self, mut neighborhood: N) -> N
where
T: 'a,
U: 'b,
N: Neighborhood<&'a T, &'b U>,
{
- self.0
+ for item in &self.buffer {
+ neighborhood.consider(item);
+ }
+
+ self.trees
.iter()
.flatten()
.fold(neighborhood, |n, t| t.search(n))