From 0052a0243d9c979a06ef273af965508103c456e0 Mon Sep 17 00:00:00 2001
From: Andres Freund <andres@anarazel.de>
Date: Tue, 22 Aug 2017 15:36:49 -0700
Subject: [PATCH] Add a hash_combine function for mixing hash values.

This hash function is derived from Boost's function of the same name.

Author: Andres Freund, Thomas Munro
Discussion: https://postgr.es/m/CAEepm%3D3rdgjfxW4cKvJ0OEmya2-34B0qHNG1xV0vK7TGPJGMUQ%40mail.gmail.com
Discussion: https://postgr.es/m/20170731210844.3cwrkmsmbbpt4rjc%40alap3.anarazel.de
---
 src/include/utils/hashutils.h | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)
 create mode 100644 src/include/utils/hashutils.h

diff --git a/src/include/utils/hashutils.h b/src/include/utils/hashutils.h
new file mode 100644
index 00000000000..56b7bfc9cb9
--- /dev/null
+++ b/src/include/utils/hashutils.h
@@ -0,0 +1,23 @@
+/*
+ * Utilities for working with hash values.
+ *
+ * Portions Copyright (c) 2017, PostgreSQL Global Development Group
+ */
+
+#ifndef HASHUTILS_H
+#define HASHUTILS_H
+
+/*
+ * Combine two hash values, resulting in another hash value, with decent bit
+ * mixing.
+ *
+ * Similar to boost's hash_combine().
+ */
+static inline uint32
+hash_combine(uint32 a, uint32 b)
+{
+	a ^= b + 0x9e3779b9 + (a << 6) + (a >> 2);
+	return a;
+}
+
+#endif							/* HASHUTILS_H */