From eac2ad7e05a576dd5e38b6672cc3c03cb4bcade0 Mon Sep 17 00:00:00 2001
From: Mathias Agopian <mathias@google.com>
Date: Fri, 9 Aug 2019 16:23:55 -0700
Subject: [PATCH] fix some lint warnings in Hash.h

---
 filament/src/fg/ResourceAllocator.h | 16 ++++++------
 libs/utils/include/utils/Hash.h     | 38 +++++++++++++++++------------
 2 files changed, 31 insertions(+), 23 deletions(-)

diff --git a/filament/src/fg/ResourceAllocator.h b/filament/src/fg/ResourceAllocator.h
index ffc84c983c..a0e7a6d0fb 100644
--- a/filament/src/fg/ResourceAllocator.h
+++ b/filament/src/fg/ResourceAllocator.h
@@ -90,14 +90,14 @@ private:
 
         friend size_t hash_value(TextureKey const& k) {
             size_t seed = 0;
-            utils::hash::hash_combine(seed, k.target);
-            utils::hash::hash_combine(seed, k.levels);
-            utils::hash::hash_combine(seed, k.format);
-            utils::hash::hash_combine(seed, k.samples);
-            utils::hash::hash_combine(seed, k.width);
-            utils::hash::hash_combine(seed, k.height);
-            utils::hash::hash_combine(seed, k.depth);
-            utils::hash::hash_combine(seed, k.usage);
+            utils::hash::combine_fast(seed, k.target);
+            utils::hash::combine_fast(seed, k.levels);
+            utils::hash::combine_fast(seed, k.format);
+            utils::hash::combine_fast(seed, k.samples);
+            utils::hash::combine_fast(seed, k.width);
+            utils::hash::combine_fast(seed, k.height);
+            utils::hash::combine_fast(seed, k.depth);
+            utils::hash::combine_fast(seed, k.usage);
             return seed;
         }
     };
diff --git a/libs/utils/include/utils/Hash.h b/libs/utils/include/utils/Hash.h
index 1487afa090..a2de76d353 100644
--- a/libs/utils/include/utils/Hash.h
+++ b/libs/utils/include/utils/Hash.h
@@ -23,39 +23,47 @@
 namespace utils {
 namespace hash {
 
-inline uint32_t murmur3(const uint32_t* key, size_t wordCount, uint32_t seed) {
+inline uint32_t murmur3(const uint32_t* key, size_t wordCount, uint32_t seed) noexcept {
     uint32_t h = seed;
     size_t i = wordCount;
     do {
         uint32_t k = *key++;
-        k *= 0xcc9e2d51;
-        k = (k << 15) | (k >> 17);
-        k *= 0x1b873593;
+        k *= 0xcc9e2d51u;
+        k = (k << 15u) | (k >> 17u);
+        k *= 0x1b873593u;
         h ^= k;
-        h = (h << 13) | (h >> 19);
-        h = (h * 5) + 0xe6546b64;
+        h = (h << 13u) | (h >> 19u);
+        h = (h * 5u) + 0xe6546b64u;
     } while (--i);
     h ^= wordCount;
-    h ^= h >> 16;
-    h *= 0x85ebca6b;
-    h ^= h >> 13;
-    h *= 0xc2b2ae35;
-    h ^= h >> 16;
+    h ^= h >> 16u;
+    h *= 0x85ebca6bu;
+    h ^= h >> 13u;
+    h *= 0xc2b2ae35u;
+    h ^= h >> 16u;
     return h;
 }
 
 template<typename T>
 struct MurmurHashFn {
-    uint32_t operator()(const T& key) const {
-        static_assert(0 == (sizeof(key) & 3), "Hashing requires a size that is a multiple of 4.");
+    uint32_t operator()(const T& key) const noexcept {
+        static_assert(0 == (sizeof(key) & 3u), "Hashing requires a size that is a multiple of 4.");
         return murmur3((const uint32_t*) &key, sizeof(key) / 4, 0);
     }
 };
 
+// combines two hashes together
 template<class T>
-inline void hash_combine(size_t& seed, const T& v) {
+inline void combine(size_t& seed, const T& v) noexcept {
     std::hash<T> hasher;
-    seed ^= hasher(v) + 0x9e3779b9 + (seed << 6u) + (seed >> 2u);
+    seed ^= hasher(v) + 0x9e3779b9u + (seed << 6u) + (seed >> 2u);
+}
+
+// combines two hashes together, faster but less good
+template<class T>
+inline void combine_fast(size_t& seed, const T& v) noexcept {
+    std::hash<T> hasher;
+    seed ^= hasher(v) << 1u;
 }
 
 } // namespace hash