From 2a0ca001e2fffcf216995a7fbf1724cc0520affe Mon Sep 17 00:00:00 2001
From: Nathan Vegdahl <cessen@cessen.com>
Date: Sat, 29 Jun 2019 12:39:28 +0900
Subject: [PATCH] Optimized ray stack task duplication with memcopy.

---
 Cargo.lock |  7 +++++++
 Cargo.toml |  1 +
 src/ray.rs | 13 ++++++++++---
 3 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index bc8f7b6..7e4b4ef 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -100,6 +100,11 @@ dependencies = [
 name = "color"
 version = "0.1.0"
 
+[[package]]
+name = "copy_in_place"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "crossbeam"
 version = "0.3.2"
@@ -239,6 +244,7 @@ dependencies = [
  "bvh_order 0.1.0",
  "clap 2.33.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "color 0.1.0",
+ "copy_in_place 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "crossbeam 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "float4 0.1.0",
  "half 1.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -557,6 +563,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum cfg-if 0.1.9 (registry+https://github.com/rust-lang/crates.io-index)" = "b486ce3ccf7ffd79fdeb678eac06a9e6c09fc88d33836340becb8fffe87c5e33"
 "checksum clap 2.33.0 (registry+https://github.com/rust-lang/crates.io-index)" = "5067f5bb2d80ef5d68b4c87db81601f0b75bca627bc2ef76b141d7b846a3c6d9"
 "checksum cloudabi 0.0.3 (registry+https://github.com/rust-lang/crates.io-index)" = "ddfc5b9aa5d4507acaf872de71051dfd0e309860e88966e1051e462a077aac4f"
+"checksum copy_in_place 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "b792a46b1ef44bb5e9a04721d34e186522431be965a283437107843d62ddbaad"
 "checksum crossbeam 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)" = "24ce9782d4d5c53674646a6a4c1863a21a8fc0cb649b3c94dfc16e45071dea19"
 "checksum fnv 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)" = "2fad85553e09a6f881f739c29f0b00b0f01357c743266d478b68951ce23285f3"
 "checksum fuchsia-cprng 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "a06f77d526c1a601b7c4cdd98f54b5eaabffc14d5f2f0296febdc7f357c6d3ba"
diff --git a/Cargo.toml b/Cargo.toml
index 1e51807..14ee2ac 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -25,6 +25,7 @@ debug = true
 # Crates.io dependencies
 base64 = "0.9"
 clap = "2.30"
+copy_in_place = "0.2.0"
 crossbeam = "0.3"
 half = "1.0"
 lazy_static = "1.0"
diff --git a/src/ray.rs b/src/ray.rs
index 97bdd39..9727522 100644
--- a/src/ray.rs
+++ b/src/ray.rs
@@ -279,11 +279,18 @@ impl RayStack {
         let start = task.start_idx;
         let end = self.lanes[l].end_len;
 
-        for i in start..end {
-            let idx = self.lanes[l].idxs[i];
-            self.lanes[l].idxs.push(idx);
+        // Extend the indices vector
+        self.lanes[l].idxs.reserve(end - start);
+        let old_len = self.lanes[l].idxs.len();
+        let new_len = old_len + end - start;
+        unsafe {
+            self.lanes[l].idxs.set_len(new_len);
         }
 
+        // Copy elements
+        copy_in_place::copy_in_place(&mut self.lanes[l].idxs, start..end, end);
+
+        // Push the new task onto the stack
         self.tasks.push(RayTask {
             lane: l,
             start_idx: end,