From 6b6334ce8e0d1076f44ec786a06c8ee4e2757746 Mon Sep 17 00:00:00 2001
From: Dieter Dobbelaere <dieter.dobbelaere@gmail.com>
Date: Sun, 8 Feb 2026 15:15:59 +0100
Subject: [PATCH] Replace FNV-1a hash by faster and better MurmurHash64A.

Replace FNV-1a hash algorithm by public domain MurmurHash64A, by Austin
Appleby, which is faster and has better hash properties. This is also
the default hash algorithm of GNU C++ Standard Library.

Startup time on a given system (with x86-64-avx2 binaries) reduces from
378ms to 332ms (46ms faster). Hashing of the largest data input (46.1MB)
goes from 44.2ms to 6.2ms, so about 7x faster.

No functional change

closes https://github.com/official-stockfish/Stockfish/pull/6579

Bench: 2570943
---
 src/misc.cpp | 39 +++++++++++++++++++++++++++++++++++++++
 src/misc.h   |  9 +--------
 2 files changed, 40 insertions(+), 8 deletions(-)

diff --git a/src/misc.cpp b/src/misc.cpp
index 3ddae503c..e0c8351fa 100644
--- a/src/misc.cpp
+++ b/src/misc.cpp
@@ -428,6 +428,45 @@ std::ostream& operator<<(std::ostream& os, SyncCout sc) {
 void sync_cout_start() { std::cout << IO_LOCK; }
 void sync_cout_end() { std::cout << IO_UNLOCK; }
 
+// Hash function based on public domain MurmurHash64A, by Austin Appleby.
+uint64_t hash_bytes(const char* data, size_t size) {
+    const uint64_t m = 0xc6a4a7935bd1e995ull;
+    const int      r = 47;
+
+    uint64_t h = size * m;
+
+    const char* end = data + (size & ~(size_t) 7);
+
+    for (const char* p = data; p != end; p += 8)
+    {
+        uint64_t k;
+        std::memcpy(&k, p, sizeof(k));
+
+        k *= m;
+        k ^= k >> r;
+        k *= m;
+
+        h ^= k;
+        h *= m;
+    }
+
+    if (size & 7)
+    {
+        uint64_t k = 0;
+        for (int i = (size & 7) - 1; i >= 0; i--)
+            k = (k << 8) | (uint64_t) end[i];
+
+        h ^= k;
+        h *= m;
+    }
+
+    h ^= h >> r;
+    h *= m;
+    h ^= h >> r;
+
+    return h;
+}
+
 // Trampoline helper to avoid moving Logger to misc.h
 void start_logger(const std::string& fname) { Logger::start(fname); }
 
diff --git a/src/misc.h b/src/misc.h
index ff9d2c284..f7a2bcf2a 100644
--- a/src/misc.h
+++ b/src/misc.h
@@ -306,14 +306,7 @@ inline uint64_t mul_hi64(uint64_t a, uint64_t b) {
 #endif
 }
 
-inline std::uint64_t hash_bytes(const char* data, std::size_t size) {
-    // FNV-1a 64-bit
-    const char*   p = data;
-    std::uint64_t h = 14695981039346656037ull;
-    for (std::size_t i = 0; i < size; ++i)
-        h = (h ^ p[i]) * 1099511628211ull;
-    return h;
-}
+uint64_t hash_bytes(const char*, size_t);
 
 template<typename T>
 inline std::size_t get_raw_data_hash(const T& value) {