add naive edge buffer

Cargo.toml

@@ -58,3 +58,7 @@ rustdoc-args = ["--cfg", "doc_cfg"]
 # Not run during tests
 [[example]]
 name = "tree_traversals"
+
+[[example]]
+name = "haploid_wright_fisher_simple_edge_buffer"
+features = ["bindings"]

examples/haploid_wright_fisher_simple_edge_buffer.rs

@@ -0,0 +1,196 @@
+// This is a rust implementation of the example
+// found in tskit-c
+
+use std::collections::HashMap;
+
+use anyhow::Result;
+use clap::Parser;
+#[cfg(test)]
+use rand::distributions::Distribution;
+use rand::prelude::*;
+use rand::SeedableRng;
+
+#[derive(Debug)]
+struct Edge {
+    left: tskit::Position,
+    right: tskit::Position,
+    child: tskit::NodeId,
+    previous: Option<usize>,
+}
+
+#[derive(Default)]
+struct EdgeBuffer {
+    parent: Vec<tskit::NodeId>,
+    last: HashMap<tskit::NodeId, usize>,
+    edges: Vec<Edge>,
+}
+
+impl EdgeBuffer {
+    fn buffer_edge(
+        &mut self,
+        left: tskit::Position,
+        right: tskit::Position,
+        parent: tskit::NodeId,
+        child: tskit::NodeId,
+    ) -> Result<()> {
+        if let Some(last) = self.last.get_mut(&parent) {
+            let pchild = self.edges[*last].child;
+            assert!(child >= pchild);
+            self.edges.push(Edge {
+                left,
+                right,
+                child,
+                previous: Some(*last),
+            });
+            *last = self.edges.len() - 1;
+        } else {
+            self.edges.push(Edge {
+                left,
+                right,
+                child,
+                previous: None,
+            });
+            self.last.insert(parent, self.edges.len() - 1);
+            self.parent.push(parent);
+        }
+        Ok(())
+    }
+
+    fn clear(&mut self) {
+        self.parent.clear();
+        self.last.clear();
+        self.edges.clear();
+    }
+}
+
+fn rotate_edges(bookmark: &tskit::types::Bookmark, tables: &mut tskit::TableCollection) {
+    let num_edges = tables.edges().num_rows().as_usize();
+    let left =
+        unsafe { std::slice::from_raw_parts_mut((*tables.as_mut_ptr()).edges.left, num_edges) };
+    let right =
+        unsafe { std::slice::from_raw_parts_mut((*tables.as_mut_ptr()).edges.right, num_edges) };
+    let parent =
+        unsafe { std::slice::from_raw_parts_mut((*tables.as_mut_ptr()).edges.parent, num_edges) };
+    let child =
+        unsafe { std::slice::from_raw_parts_mut((*tables.as_mut_ptr()).edges.child, num_edges) };
+    let mid = bookmark.edges().as_usize();
+    left.rotate_left(mid);
+    right.rotate_left(mid);
+    parent.rotate_left(mid);
+    child.rotate_left(mid);
+}
+
+// ANCHOR: haploid_wright_fisher
+fn simulate(
+    seed: u64,
+    popsize: usize,
+    num_generations: i32,
+    simplify_interval: i32,
+) -> Result<tskit::TreeSequence> {
+    if popsize == 0 {
+        return Err(anyhow::Error::msg("popsize must be > 0"));
+    }
+    if num_generations == 0 {
+        return Err(anyhow::Error::msg("num_generations must be > 0"));
+    }
+    if simplify_interval == 0 {
+        return Err(anyhow::Error::msg("simplify_interval must be > 0"));
+    }
+    let mut tables = tskit::TableCollection::new(1.0)?;
+
+    // create parental nodes
+    let mut parents_and_children = {
+        let mut temp = vec![];
+        let parental_time = f64::from(num_generations);
+        for _ in 0..popsize {
+            let node = tables.add_node(0, parental_time, -1, -1)?;
+            temp.push(node);
+        }
+        temp
+    };
+
+    // allocate space for offspring nodes
+    parents_and_children.resize(2 * parents_and_children.len(), tskit::NodeId::NULL);
+
+    // Construct non-overlapping mutable slices into our vector.
+    let (mut parents, mut children) = parents_and_children.split_at_mut(popsize);
+
+    let parent_picker = rand::distributions::Uniform::new(0, popsize);
+    let breakpoint_generator = rand::distributions::Uniform::new(0.0, 1.0);
+    let mut rng = rand::rngs::StdRng::seed_from_u64(seed);
+    let mut bookmark = tskit::types::Bookmark::default();
+
+    let mut buffer = EdgeBuffer::default();
+    for birth_time in (0..num_generations).rev() {
+        for c in children.iter_mut() {
+            let bt = f64::from(birth_time);
+            let child = tables.add_node(0, bt, -1, -1)?;
+            let left_parent = parents
+                .get(parent_picker.sample(&mut rng))
+                .ok_or_else(|| anyhow::Error::msg("invalid left_parent index"))?;
+            let right_parent = parents
+                .get(parent_picker.sample(&mut rng))
+                .ok_or_else(|| anyhow::Error::msg("invalid right_parent index"))?;
+            let breakpoint = breakpoint_generator.sample(&mut rng);
+            buffer.buffer_edge(0_f64.into(), breakpoint.into(), *left_parent, child)?;
+            buffer.buffer_edge(breakpoint.into(), 1_f64.into(), *right_parent, child)?;
+            *c = child;
+        }
+
+        if birth_time % simplify_interval == 0 {
+            for &parent in buffer.parent.iter().rev() {
+                let mut last = buffer.last.get(&parent).cloned();
+                while let Some(previous) = last {
+                    let edge = &buffer.edges[previous];
+                    tables.add_edge(edge.left, edge.right, parent, edge.child)?;
+                    last = edge.previous;
+                }
+            }
+            buffer.clear();
+            rotate_edges(&bookmark, &mut tables);
+            if let Some(idmap) =
+                tables.simplify(children, tskit::SimplificationOptions::default(), true)?
+            {
+                // remap child nodes
+                for o in children.iter_mut() {
+                    *o = idmap[usize::try_from(*o)?];
+                }
+            }
+            bookmark.set_edges(tables.edges().num_rows());
+        }
+        std::mem::swap(&mut parents, &mut children);
+    }
+
+    tables.build_index()?;
+    let treeseq = tables.tree_sequence(tskit::TreeSequenceFlags::default())?;
+
+    Ok(treeseq)
+}
+// ANCHOR_END: haploid_wright_fisher
+
+#[derive(Clone, clap::Parser)]
+struct SimParams {
+    seed: u64,
+    popsize: usize,
+    num_generations: i32,
+    simplify_interval: i32,
+    treefile: Option<String>,
+    #[clap(short, long, help = "Use bookmark to avoid sorting entire edge table.")]
+    bookmark: bool,
+}
+
+fn main() -> Result<()> {
+    let params = SimParams::parse();
+    let treeseq = simulate(
+        params.seed,
+        params.popsize,
+        params.num_generations,
+        params.simplify_interval,
+    )?;
+
+    if let Some(treefile) = &params.treefile {
+        treeseq.dump(treefile, 0)?;
+    }
+
+    Ok(())
+}