From 7082f2d7f4a48e6eaa281961bd10b290270bf05f Mon Sep 17 00:00:00 2001
From: Nathan Vegdahl <cessen@cessen.com>
Date: Thu, 21 Jul 2022 05:22:22 -0700
Subject: [PATCH] Update hash functions to known good ones instead of bespoke
 ones.

---
 src/hash.rs | 44 ++++++++++++++++++++++++++++----------------
 1 file changed, 28 insertions(+), 16 deletions(-)

diff --git a/src/hash.rs b/src/hash.rs
index 6790092..49022a9 100644
--- a/src/hash.rs
+++ b/src/hash.rs
@@ -1,23 +1,35 @@
-pub fn hash_u32(n: u32, seed: u32) -> u32 {
-    let mut hash = n;
-    for _ in 0..3 {
-        hash = hash.wrapping_mul(0x736caf6f);
-        hash ^= hash.wrapping_shr(16);
-        hash ^= seed;
-    }
+/// A fast seedable 32-bit hash function.
+///
+/// Based on <https://github.com/skeeto/hash-prospector>.
+pub fn hash_u32(mut n: u32, seed: u32) -> u32 {
+    n ^= 0xe6fe3beb; // So zero doesn't map to zero.
+    n ^= seed;
 
-    hash
+    n ^= n >> 16;
+    n = n.wrapping_mul(0x21f0aaad);
+    n ^= seed;
+    n ^= n >> 15;
+    n = n.wrapping_mul(0xd35a2d97);
+    n ^= n >> 15;
+
+    n
 }
 
-pub fn hash_u64(n: u64, seed: u64) -> u64 {
-    let mut hash = n;
-    for _ in 0..4 {
-        hash = hash.wrapping_mul(32_416_190_071 * 314_604_959);
-        hash ^= hash.wrapping_shr(32);
-        hash ^= seed;
-    }
+/// A fast seedable 64-bit hash function.
+///
+/// Based on <https://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html>.
+pub fn hash_u64(mut n: u64, seed: u64) -> u64 {
+    n ^= 0x4acc3f27cc712c9d; // So zero doesn't map to zero.
+    n ^= seed;
 
-    hash
+    n ^= n >> 30;
+    n = n.wrapping_mul(0xbf58476d1ce4e5b9);
+    n ^= seed;
+    n ^= n >> 27;
+    n = n.wrapping_mul(0x94d049bb133111eb);
+    n ^= n >> 31;
+
+    n
 }
 
 /// Returns a random float in [0, 1] based on 'n' and a seed.