Added test_murmur_hash_128_3(). Also fixed an endianness error in the hashing

unit test code.

dlib/general_hash/murmur_hash3.h

@@ -372,6 +372,48 @@ namespace dlib
         return std::make_pair(h1,h2);
     }
 
+// ----------------------------------------------------------------------------------------
+
+    inline std::pair<uint64,uint64> murmur_hash3_128bit_3 ( 
+        uint64 k1, 
+        uint64 k2,
+        uint64 k3 
+    )
+    {
+        uint64 h1 = k3;
+        uint64 h2 = k3;
+
+        const uint64 c1 = DLIB_BIG_CONSTANT(0x87c37b91114253d5);
+        const uint64 c2 = DLIB_BIG_CONSTANT(0x4cf5ad432745937f);
+
+        //----------
+        // body
+
+        k1 *= c1; k1  = DLIB_ROTL64(k1,31); k1 *= c2; h1 ^= k1;
+
+        h1 = DLIB_ROTL64(h1,27); h1 += h2; h1 = h1*5+0x52dce729;
+
+        k2 *= c2; k2  = DLIB_ROTL64(k2,33); k2 *= c1; h2 ^= k2;
+
+        h2 = DLIB_ROTL64(h2,31); h2 += h1; h2 = h2*5+0x38495ab5;
+
+        //----------
+        // finalization
+
+        h1 ^= 16; h2 ^= 16;
+
+        h1 += h2;
+        h2 += h1;
+
+        h1 = murmur_fmix(h1);
+        h2 = murmur_fmix(h2);
+
+        h1 += h2;
+        h2 += h1;
+
+        return std::make_pair(h1,h2);
+    }
+
 // ----------------------------------------------------------------------------------------
 
 }

dlib/general_hash/murmur_hash3_abstract.h

@@ -68,6 +68,23 @@ namespace dlib
               See: http://code.google.com/p/smhasher/
     !*/
 
+// ----------------------------------------------------------------------------------------
+
+    std::pair<uint64,uint64> murmur_hash3_128bit_3 ( 
+        uint64 k1, 
+        uint64 k2,
+        uint64 k3 
+    );
+    /*!
+        ensures
+            - returns a 128bit hash (as two 64bit numbers) of the 3 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_x64_128.  
+              See: http://code.google.com/p/smhasher/
+    !*/
+
 // ----------------------------------------------------------------------------------------
 
 }

dlib/test/hash.cpp

@@ -110,6 +110,7 @@ namespace
 
     void test_murmur_hash_128_4()
     {
+        byte_orderer bo;
         dlib::rand rnd;
         for (int i = 0; i < 100; ++i)
         {
@@ -119,6 +120,7 @@ namespace
                 rnd.get_random_32bit_number()
             };
 
+            bo.host_to_little(buf);
             std::pair<uint64,uint64> temp1, temp2;
 
             // Make sure the 4 integer version of murmur hash does the same thing 
@@ -130,6 +132,30 @@ namespace
         }
     }
 
+    void test_murmur_hash_128_3()
+    {
+        byte_orderer bo;
+        dlib::rand rnd;
+        for (int i = 0; i < 100; ++i)
+        {
+            uint64 buf[2] = { rnd.get_random_64bit_number(), 
+                rnd.get_random_64bit_number(),
+            };
+
+            const uint32 seed = rnd.get_random_32bit_number();
+
+            bo.host_to_little(buf);
+            std::pair<uint64,uint64> temp1, temp2;
+
+            // Make sure the 3 integer version of murmur hash does the same thing 
+            // as the memory block version.
+            temp1 = murmur_hash3_128bit(buf, sizeof(buf), seed);
+            temp2 = murmur_hash3_128bit_3(buf[0], buf[1], seed);
+            DLIB_TEST( temp1.first == temp2.first);
+            DLIB_TEST( temp1.second == temp2.second);
+        }
+    }
+
     class test_hash : public tester
     {
     public:
@@ -207,6 +233,7 @@ namespace
             DLIB_TEST(murmur_hash3(&str1[0], str1.size(), 1) == 0xb17cea93);
 
             test_murmur_hash_128_4();
+            test_murmur_hash_128_3();
         }
     } a;