From edfd2290eb63ced7dd21a44d612705ae4ccfb0e1 Mon Sep 17 00:00:00 2001
From: Joshua Barretto <joshua.s.barretto@gmail.com>
Date: Mon, 13 May 2019 10:32:02 +0100
Subject: [PATCH] Massively sped up VolMap offset calculations

Former-commit-id: 8f3cdf57a77691ca60c0921bc86a79c8cfe36539
---
 common/src/state.rs           |  2 +-
 common/src/volumes/vol_map.rs | 29 ++++++++++++++++++++++-------
 2 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/common/src/state.rs b/common/src/state.rs
index 29cdb59f4a..509ca67ca7 100644
--- a/common/src/state.rs
+++ b/common/src/state.rs
@@ -110,7 +110,7 @@ impl State {
         ecs.add_resource(TimeOfDay(0.0));
         ecs.add_resource(Time(0.0));
         ecs.add_resource(DeltaTime(0.0));
-        ecs.add_resource(TerrainMap::new());
+        ecs.add_resource(TerrainMap::new().unwrap());
     }
 
     /// Register a component with the state's ECS
diff --git a/common/src/volumes/vol_map.rs b/common/src/volumes/vol_map.rs
index d73ede7ee1..aa7c297428 100644
--- a/common/src/volumes/vol_map.rs
+++ b/common/src/volumes/vol_map.rs
@@ -19,6 +19,7 @@ pub enum VolMapErr {
     NoSuchChunk,
     ChunkErr(ChunkErr),
     DynaErr(DynaErr),
+    InvalidChunkSize,
 }
 
 // V = Voxel
@@ -31,13 +32,20 @@ pub struct VolMap<V: Vox + Clone, S: VolSize + Clone, M: Clone> {
 
 impl<V: Vox + Clone, S: VolSize + Clone, M: Clone> VolMap<V, S, M> {
     #[inline(always)]
-    fn chunk_key(pos: Vec3<i32>) -> Vec3<i32> {
-        pos.map2(S::SIZE, |e, sz| e.div_euclid(sz as i32))
+    pub fn chunk_key(pos: Vec3<i32>) -> Vec3<i32> {
+        pos.map2(S::SIZE, |e, sz| {
+            // Horrid, but it's faster than a cheetah with a red bull blood transfusion
+            let log2 = (sz - 1).count_ones();
+            ((((e as i64 + (1 << 32)) as u64) >> log2) - (1 << (32 - log2))) as i32
+        })
     }
 
     #[inline(always)]
     pub fn chunk_offs(pos: Vec3<i32>) -> Vec3<i32> {
-        pos.map2(S::SIZE, |e, sz| e.rem_euclid(sz as i32))
+        pos.map2(S::SIZE, |e, sz| {
+            // Horrid, but it's even faster than the aforementioned cheetah
+            (((e as i64 + (1 << 32)) as u64) & (sz - 1) as u64) as i32
+        })
     }
 }
 
@@ -150,10 +158,17 @@ impl<V: Vox + Clone, S: VolSize + Clone, M: Clone> WriteVol for VolMap<V, S, M>
     }
 }
 
-impl<V: Vox + Clone, S: VolSize + Clone, M: Clone> VolMap<V, S, M> {
-    pub fn new() -> Self {
-        Self {
-            chunks: HashMap::new(),
+impl<V: Vox + Clone, S: VolSize + Clone, M + Clone> VolMap<V, S, M> {
+    pub fn new() -> Result<Self, VolMapErr> {
+        if Self::chunk_size()
+            .map(|e| e.is_power_of_two() && e > 0)
+            .reduce_and()
+        {
+            Ok(Self {
+                chunks: HashMap::new(),
+            })
+        } else {
+            Err(VolMapErr::InvalidChunkSize)
         }
     }