From cf49cdbb026719d49c2a806681fdef4af5c85f3b Mon Sep 17 00:00:00 2001
From: Nathan Vegdahl <cessen@cessen.com>
Date: Sun, 14 Aug 2016 16:03:17 -0700
Subject: [PATCH] Moved int hash functions into own file, and use in
 quick_select().

---
 src/algorithm.rs | 13 ++++++++++++-
 src/hash.rs      | 23 +++++++++++++++++++++++
 src/main.rs      |  1 +
 src/renderer.rs  | 14 +-------------
 4 files changed, 37 insertions(+), 14 deletions(-)
 create mode 100644 src/hash.rs

diff --git a/src/algorithm.rs b/src/algorithm.rs
index 5208691..8c81e6a 100644
--- a/src/algorithm.rs
+++ b/src/algorithm.rs
@@ -4,6 +4,7 @@ use std;
 use std::cmp;
 use std::cmp::Ordering;
 use lerp::{Lerp, lerp_slice};
+use hash::hash_u64;
 
 /// Partitions a slice in-place with the given unary predicate, returning
 /// the index of the first element for which the predicate evaluates
@@ -120,9 +121,10 @@ pub fn quick_select<T, F>(slc: &mut [T], n: usize, mut order: F)
 {
     let mut left = 0;
     let mut right = slc.len();
+    let mut seed = n as u64;
 
     loop {
-        let i = (left + right) / 2;
+        let i = left + (hash_u64(right as u64, seed) as usize % (right - left));
 
         slc.swap(i, right - 1);
         let ii = left +
@@ -139,6 +141,8 @@ pub fn quick_select<T, F>(slc: &mut [T], n: usize, mut order: F)
         } else {
             left = ii + 1;
         }
+
+        seed += 1;
     }
 }
 
@@ -241,4 +245,11 @@ mod tests {
         quick_select_ints(&mut list, 0);
         assert_eq!(list[0], 0);
     }
+
+    #[test]
+    fn quick_select_4() {
+        let mut list = [8, 9, 7, 4, 6, 1, 0, 5, 3, 2];
+        quick_select_ints(&mut list, 9);
+        assert_eq!(list[9], 9);
+    }
 }
diff --git a/src/hash.rs b/src/hash.rs
new file mode 100644
index 0000000..b9c5e0a
--- /dev/null
+++ b/src/hash.rs
@@ -0,0 +1,23 @@
+pub fn hash_u32(n: u32, seed: u32) -> u32 {
+    let mut hash = n;
+
+    for _ in 0..3 {
+        hash = hash.wrapping_mul(1936502639);
+        hash ^= hash.wrapping_shr(16);
+        hash = hash.wrapping_add(seed);
+    }
+
+    return hash;
+}
+
+pub fn hash_u64(n: u64, seed: u64) -> u64 {
+    let mut hash = n;
+
+    for _ in 0..4 {
+        hash = hash.wrapping_mul(32416190071 * 314604959);
+        hash ^= hash.wrapping_shr(32);
+        hash = hash.wrapping_add(seed);
+    }
+
+    return hash;
+}
diff --git a/src/main.rs b/src/main.rs
index 555ee18..c6688ce 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -36,6 +36,7 @@ mod scene;
 mod assembly;
 mod halton;
 mod sampling;
+mod hash;
 mod color;
 mod shading;
 
diff --git a/src/renderer.rs b/src/renderer.rs
index 28a6937..1f3f7b8 100644
--- a/src/renderer.rs
+++ b/src/renderer.rs
@@ -12,6 +12,7 @@ use ray::Ray;
 use tracer::Tracer;
 use halton;
 use hilbert;
+use hash::hash_u32;
 use math::{fast_logit, upper_power_of_two};
 use image::Image;
 use surface;
@@ -373,16 +374,3 @@ struct BucketJob {
     w: u32,
     h: u32,
 }
-
-
-fn hash_u32(n: u32, seed: u32) -> u32 {
-    let mut hash = n;
-
-    for _ in 0..3 {
-        hash = hash.wrapping_mul(1936502639);
-        hash ^= hash.wrapping_shr(16);
-        hash = hash.wrapping_add(seed);
-    }
-
-    return hash;
-}