From f9894647e308e6dd8ca8c34f86df68fb83cb21e2 Mon Sep 17 00:00:00 2001
From: lisyarus <lisyarus@gmail.com>
Date: Sun, 25 Apr 2021 22:08:42 +0300
Subject: [PATCH] Better 64-bit hash_combine

---
 libs/util/include/psemek/util/hash.hpp | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/libs/util/include/psemek/util/hash.hpp b/libs/util/include/psemek/util/hash.hpp
index 4e6a1e9c..a2ae01e8 100644
--- a/libs/util/include/psemek/util/hash.hpp
+++ b/libs/util/include/psemek/util/hash.hpp
@@ -6,10 +6,14 @@
 namespace psemek::util
 {
 
-	// based on boost::hash_combine
 	inline void hash_combine(std::size_t & seed, std::size_t value)
 	{
-		seed ^= value + 0x9e3779b9 + (seed<<6) + (seed>>2);
+		static const std::size_t k = 0x9ddfea08eb382d69ULL;
+		std::size_t a = (value ^ seed) * k;
+		a ^= (a >> 47);
+		std::size_t b = (seed ^ a) * k;
+		b ^= (b >> 47);
+		seed = b * k;
 	}
 
 }