From e0d4aa1e7b014ced152ce16c71e9f57180d42935 Mon Sep 17 00:00:00 2001
From: kaetemi <kaetemi@gmail.com>
Date: Sun, 29 Mar 2015 03:14:06 +0200
Subject: [PATCH] Add Wang hash functions

--HG--
branch : develop
---
 code/nel/include/nel/misc/wang_hash.h | 74 +++++++++++++++++++++++++++
 1 file changed, 74 insertions(+)
 create mode 100644 code/nel/include/nel/misc/wang_hash.h

diff --git a/code/nel/include/nel/misc/wang_hash.h b/code/nel/include/nel/misc/wang_hash.h
new file mode 100644
index 000000000..b3069b92f
--- /dev/null
+++ b/code/nel/include/nel/misc/wang_hash.h
@@ -0,0 +1,74 @@
+// Public domain hash functions
+
+#ifndef NLMISC_WANG_HASH_H
+#define NLMISC_WANG_HASH_H
+
+#include "types_nl.h"
+
+namespace NLMISC {
+
+// http://burtleburtle.net/bob/hash/integer.html
+inline uint32 wangHash(uint32 a)
+{
+	a = (a ^ 61) ^ (a >> 16);
+	a = a + (a << 3);
+	a = a ^ (a >> 4);
+	a = a * 0x27d4eb2d;
+	a = a ^ (a >> 15);
+	return a;
+}
+
+// http://naml.us/blog/2012/03
+inline uint64 wangHash64(uint64 key)
+{
+	key = (~key) + (key << 21); // key = (key << 21) - key - 1;
+	key = key ^ (key >> 24);
+	key = (key + (key << 3)) + (key << 8); // key * 265
+	key = key ^ (key >> 14);
+	key = (key + (key << 2)) + (key << 4); // key * 21
+	key = key ^ (key >> 28);
+	key = key + (key << 31);
+	return key;
+}
+
+// http://naml.us/blog/2012/03 Inverse 64-bit wang hash
+inline uint64 wangHash64Inv(uint64 key)
+{
+	uint64 tmp;
+
+	// Invert key = key + (key << 31)
+	tmp = key - (key << 31);
+	key = key - (tmp << 31);
+
+	// Invert key = key ^ (key >> 28)
+	tmp = key^key >> 28;
+	key = key^tmp >> 28;
+
+	// Invert key *= 21
+	key *= 14933078535860113213u;
+
+	// Invert key = key ^ (key >> 14)
+	tmp = key^key >> 14;
+	tmp = key^tmp >> 14;
+	tmp = key^tmp >> 14;
+	key = key^tmp >> 14;
+
+	// Invert key *= 265
+	key *= 15244667743933553977u;
+
+	// Invert key = key ^ (key >> 24)
+	tmp = key^key >> 24;
+	key = key^tmp >> 24;
+
+	// Invert key = (~key) + (key << 21)
+	tmp = ~key;
+	tmp = ~(key - (tmp << 21));
+	tmp = ~(key - (tmp << 21));
+	key = ~(key - (tmp << 21));
+
+	return key;
+}
+
+} /* namespace NLMISC */
+
+#endif // NLMISC_WANG_HASH_H