From 49f2d6f9dffbe6b68ab3778b53ad7902683bd4e5 Mon Sep 17 00:00:00 2001
From: Davis King <davis@dlib.net>
Date: Tue, 27 Nov 2012 20:45:35 -0500
Subject: [PATCH] Added murmur_hash3_2()

---
 dlib/general_hash/murmur_hash3.h          | 37 +++++++++++++++++++++++
 dlib/general_hash/murmur_hash3_abstract.h | 15 +++++++++
 dlib/test/hash.cpp                        | 22 ++++++++++++++
 3 files changed, 74 insertions(+)

diff --git a/dlib/general_hash/murmur_hash3.h b/dlib/general_hash/murmur_hash3.h
index 353ac4fe2..ab4f77005 100644
--- a/dlib/general_hash/murmur_hash3.h
+++ b/dlib/general_hash/murmur_hash3.h
@@ -218,6 +218,43 @@ namespace dlib
         return h1;
     } 
 
+// ----------------------------------------------------------------------------------------
+
+    inline uint32 murmur_hash3_2 ( 
+        const uint32 v1,
+        const uint32 v2 
+    )
+    {
+        uint32 h1 = v2;
+
+        uint32 c1 = 0xcc9e2d51;
+        uint32 c2 = 0x1b873593;
+
+        //----------
+        // body
+
+
+        uint32 k1 = v1;
+
+        k1 *= c1;
+        k1 = DLIB_ROTL32(k1,15);
+        k1 *= c2;
+
+        h1 ^= k1;
+        h1 = DLIB_ROTL32(h1,13); 
+        h1 = h1*5+0xe6546b64;
+
+
+        //----------
+        // finalization
+
+        h1 ^= 4; // =^ by length in bytes
+
+        h1 = murmur_fmix(h1);
+
+        return h1;
+    } 
+
 // ----------------------------------------------------------------------------------------
 
     inline std::pair<uint64,uint64> murmur_hash3_128bit ( 
diff --git a/dlib/general_hash/murmur_hash3_abstract.h b/dlib/general_hash/murmur_hash3_abstract.h
index 726d45eda..05fd7c42e 100644
--- a/dlib/general_hash/murmur_hash3_abstract.h
+++ b/dlib/general_hash/murmur_hash3_abstract.h
@@ -29,6 +29,21 @@ namespace dlib
               See: http://code.google.com/p/smhasher/
     !*/
 
+// ----------------------------------------------------------------------------------------
+
+    inline uint32 murmur_hash3_2 ( 
+        const uint32 v1,
+        const uint32 v2 
+    );
+    /*!
+        ensures
+            - returns a 32bit hash of the two integers given to this function.  
+            - This function is machine architecture agnostic and should always give the same
+              hash value when presented with the same inputs.
+            - This hashing algorithm is Austin Appleby's excellent MurmurHash3_x86_32.  
+              See: http://code.google.com/p/smhasher/
+    !*/
+
 // ----------------------------------------------------------------------------------------
 
     std::pair<uint64,uint64> murmur_hash3_128bit ( 
diff --git a/dlib/test/hash.cpp b/dlib/test/hash.cpp
index 66ce70c49..4635e9825 100644
--- a/dlib/test/hash.cpp
+++ b/dlib/test/hash.cpp
@@ -162,6 +162,27 @@ namespace
         }
     }
 
+    void test_murmur_hash_64_2()
+    {
+        byte_orderer bo;
+        dlib::rand rnd;
+        for (int i = 0; i < 100; ++i)
+        {
+            uint32 val = rnd.get_random_32bit_number();
+            const uint32 seed = rnd.get_random_32bit_number();
+
+
+            bo.host_to_little(val);
+            uint32 temp1, temp2;
+
+            // Make sure the 2 integer version of murmur hash does the same thing 
+            // as the memory block version.
+            temp1 = murmur_hash3(&val, sizeof(val), seed);
+            temp2 = murmur_hash3_2(val, seed);
+            DLIB_TEST(temp1 == temp2);
+        }
+    }
+
     class test_hash : public tester
     {
     public:
@@ -240,6 +261,7 @@ namespace
 
             test_murmur_hash_128_4();
             test_murmur_hash_128_3();
+            test_murmur_hash_64_2();
         }
     } a;