From d9238aabf22497024b52c68c31c42c8e9c0a17e6 Mon Sep 17 00:00:00 2001
From: stuefe <unknown>
Date: Thu, 14 May 2020 08:48:36 +0200
Subject: [PATCH] 8244777: ClassLoaderStats VM Op uses constant hash value
 Reviewed-by: coleenp, jbachorik

---
 src/share/vm/classfile/classLoaderStats.hpp | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/share/vm/classfile/classLoaderStats.hpp b/src/share/vm/classfile/classLoaderStats.hpp
index 72904c12d..b9e0fc2cd 100644
--- a/src/share/vm/classfile/classLoaderStats.hpp
+++ b/src/share/vm/classfile/classLoaderStats.hpp
@@ -101,8 +101,17 @@ protected:
   }
 
   static unsigned oop_hash(oop const& s1) {
-    unsigned hash = (unsigned)((uintptr_t)&s1);
-    return hash ^ (hash >> LogMinObjAlignment);
+    // Robert Jenkins 1996 & Thomas Wang 1997
+    // http://web.archive.org/web/20071223173210/http://www.concentric.net/~Ttwang/tech/inthash.htm
+    uintptr_t tmp = cast_from_oop<uintptr_t>(s1);
+    unsigned hash = (unsigned)tmp;
+    hash = ~hash + (hash << 15);
+    hash = hash ^ (hash >> 12);
+    hash = hash + (hash << 2);
+    hash = hash ^ (hash >> 4);
+    hash = hash * 2057;
+    hash = hash ^ (hash >> 16);
+    return hash;
   }
 
   typedef ResourceHashtable<oop, ClassLoaderStats*,
-- 
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