From 2786e28577cb60782296b0636b7c4519aa3c75a9 Mon Sep 17 00:00:00 2001
From: Acrimon <joel.wejdenstal@gmail.com>
Date: Tue, 17 Sep 2019 16:56:23 +0200
Subject: [PATCH] Fixed rng stuff.

---
 world/src/util/hash_cache.rs |  2 +-
 world/src/util/random.rs     | 28 +++-------------------------
 world/src/util/seed_expan.rs | 11 ++++++++++-
 3 files changed, 14 insertions(+), 27 deletions(-)

diff --git a/world/src/util/hash_cache.rs b/world/src/util/hash_cache.rs
index 2abe5c8cd7..9e46ebe807 100644
--- a/world/src/util/hash_cache.rs
+++ b/world/src/util/hash_cache.rs
@@ -17,7 +17,7 @@ impl<K: Hash + Eq + Clone, V> HashCache<K, V> {
     pub fn with_capacity(capacity: usize) -> Self {
         Self {
             capacity,
-            map: HashMap::default(),
+            map: HashMap::with_capacity(1024),
             counter: 0,
         }
     }
diff --git a/world/src/util/random.rs b/world/src/util/random.rs
index da56a76ee2..3192138063 100644
--- a/world/src/util/random.rs
+++ b/world/src/util/random.rs
@@ -1,5 +1,6 @@
 use super::Sampler;
 use vek::*;
+use super::seed_expan;
 
 pub struct RandomField {
     seed: u32,
@@ -17,22 +18,7 @@ impl Sampler<'static> for RandomField {
 
     fn get(&self, pos: Self::Index) -> Self::Sample {
         let pos = pos.map(|e| u32::from_le_bytes(e.to_le_bytes()));
-
-        let mut a = self.seed;
-        a = (a ^ 61) ^ (a >> 16);
-        a = a.wrapping_add(a << 3);
-        a = a ^ pos.x;
-        a = a ^ (a >> 4);
-        a = a.wrapping_mul(0x27d4eb2d);
-        a = a ^ (a >> 15);
-        a = a ^ pos.y;
-        a = (a ^ 61) ^ (a >> 16);
-        a = a.wrapping_add(a << 3);
-        a = a ^ (a >> 4);
-        a = a ^ pos.z;
-        a = a.wrapping_mul(0x27d4eb2d);
-        a = a ^ (a >> 15);
-        a
+        seed_expan::diffuse_mult(&[self.seed, pos.x, pos.y, pos.z])
     }
 }
 
@@ -51,14 +37,6 @@ impl Sampler<'static> for RandomPerm {
     type Sample = u32;
 
     fn get(&self, perm: Self::Index) -> Self::Sample {
-        let a = self
-            .seed
-            .wrapping_mul(3471)
-            .wrapping_add(perm)
-            .wrapping_add(0x3BE7172B)
-            .wrapping_mul(perm)
-            .wrapping_add(0x172A3BE1);
-        let b = a.wrapping_mul(a);
-        b ^ (a >> 17) ^ b >> 15
+        seed_expan::diffuse_mult(&[self.seed, perm])
     }
 }
diff --git a/world/src/util/seed_expan.rs b/world/src/util/seed_expan.rs
index ceee6acd56..30338eca64 100644
--- a/world/src/util/seed_expan.rs
+++ b/world/src/util/seed_expan.rs
@@ -20,10 +20,19 @@ pub fn diffuse(mut x: u32) -> u32 {
     x = x.wrapping_add(0xd3a2646c) ^ (x << 9);
     x = x.wrapping_add(0xfd7046c5).wrapping_add(x << 3);
     x = (x ^ 0xb55a4f09) ^ (x >> 16);
-    x = x.wrapping_add((1 << 31) - 1) ^ (x << 13);
+    x = x.wrapping_add((1 << 31) - 13) ^ (x << 13);
     x
 }
 
+/// Diffuse but takes multiple values as input.
+pub fn diffuse_mult(v: &[u32]) -> u32 {
+    let mut state = (1 << 31) - 1;
+    for e in v {
+        state = diffuse(state ^ e);
+    }
+    state
+}
+
 /// Expand a 32 bit seed into a 32 byte RNG state.
 pub fn rng_state(mut x: u32) -> [u8; 32] {
     let mut r: [u32; 8] = [0; 8];