Renamed "forge" to "spark". Updated meta-references and future domain. (#40)

rust/spark-internal-rs/src/sort.rs

@@ -0,0 +1,67 @@
+use anyhow::anyhow;
+
+const DEPTH_INFINITY: u32 = 0x7c00;
+const DEPTH_SIZE: usize = DEPTH_INFINITY as usize + 1;
+
+#[derive(Default)]
+pub struct SortBuffers {
+    pub readback: Vec<u16>,
+    pub ordering: Vec<u32>,
+    pub buckets: Vec<u32>,
+}
+
+impl SortBuffers {
+    pub fn ensure_size(&mut self, max_splats: usize) {
+        if self.readback.len() < max_splats {
+            self.readback.resize(max_splats, 0);
+        }
+        if self.ordering.len() < max_splats {
+            self.ordering.resize(max_splats, 0);
+        }
+        if self.buckets.len() < DEPTH_SIZE {
+            self.buckets.resize(DEPTH_SIZE, 0);
+        }
+    }
+}
+
+pub fn sort_internal(buffers: &mut SortBuffers, num_splats: usize) -> anyhow::Result<u32> {
+    let SortBuffers { readback, ordering, buckets } = buffers;
+    let readback = &readback[..num_splats];
+
+    // Set the bucket counts to zero
+    buckets.clear();
+    buckets.resize(DEPTH_SIZE, 0);
+
+    // Count the number of splats in each bucket
+    for &metric in readback.iter() {
+        if (metric as u32) < DEPTH_INFINITY {
+            buckets[metric as usize] += 1;
+        }
+    }
+
+    // Compute bucket starting offset
+    let mut active_splats = 0;
+    for count in buckets.iter_mut().rev().skip(1) {
+        let new_total = active_splats + *count;
+        *count = active_splats;
+        active_splats = new_total;
+    }
+
+    // Write out splat indices at the right location using bucket offsets
+    for (index, &metric) in readback.iter().enumerate() {
+        if (metric as u32) < DEPTH_INFINITY {
+            ordering[buckets[metric as usize] as usize] = index as u32;
+            buckets[metric as usize] += 1;
+        }
+    }
+
+    // Sanity check
+    if buckets[0] != active_splats {
+        return Err(anyhow!(
+            "Expected {} active splats but got {}",
+            active_splats,
+            buckets[0]
+        ));
+    }
+    Ok(active_splats)
+}