Added a hash() for matrices.

dlib/matrix/matrix_utilities.h

@@ -16,6 +16,7 @@
 #include "matrix_expressions.h"
 #include "matrix_math_functions.h"
 #include "matrix_op.h"
+#include "../general_hash/murmur_hash3.h"
 
 
 namespace dlib
@@ -3966,6 +3967,22 @@ namespace dlib
         return matrix_op<op>(op(m.ref()));
     }
 
+// ----------------------------------------------------------------------------------------
+
+    template <typename T, long NR, long NC, typename MM, typename L>
+    uint32 hash (
+        const matrix<T,NR,NC,MM,L>& item,
+        uint32 seed = 0
+    )
+    {
+        DLIB_ASSERT_HAS_STANDARD_LAYOUT(T);
+
+        if (item.size() == 0)
+            return 0;
+        else
+            return murmur_hash3(&item(0,0), sizeof(T)*item.size(), seed);
+    }
+
 // ----------------------------------------------------------------------------------------
 
 }

dlib/matrix/matrix_utilities_abstract.h

@@ -667,10 +667,11 @@ namespace dlib
         long NR,
         long NC,
         typename MM,
-        typename U
+        typename U,
+        typename L
         >
     void set_all_elements (
-        matrix<T,NR,NC,MM>& m,
+        matrix<T,NR,NC,MM,L>& m,
         U value
     );
     /*!
@@ -690,6 +691,27 @@ namespace dlib
               (This allows you to easily force a matrix_exp to fully evaluate)
     !*/
 
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename T, 
+        long NR, 
+        long NC, 
+        typename MM, 
+        typename L
+        >
+    uint32 hash (
+        const matrix<T,NR,NC,MM,L>& item,
+        uint32 seed = 0
+    );
+    /*!
+        ensures
+            - returns a 32bit hash of the data stored in item.  
+            - Each value of seed results in a different hash function being used.  
+              (e.g. hash(item,0) should generally not be equal to hash(item,1))
+            - uses the murmur_hash3() routine to compute the actual hash.
+    !*/
+
 // ----------------------------------------------------------------------------------------
 
     // if matrix_exp contains non-complex types (e.g. float, double)

dlib/test/hash.cpp

@@ -6,6 +6,7 @@
 #include <cstdlib>
 #include <ctime>
 #include <dlib/hash.h>
+#include <dlib/matrix.h>
 
 #include "tester.h"
 
@@ -32,6 +33,9 @@ namespace
         {
             std::string str1 = "some random string";
             std::wstring str2 = L"another String!";
+            matrix<unsigned char> mat(2,2);
+
+            mat = 1,2,3,4;
 
             std::vector<unsigned char> v(4);
             v[0] = 'c';
@@ -48,22 +52,26 @@ namespace
             dlog << LINFO << "hash(str2): "<< hash(str2);
             dlog << LINFO << "hash(v): "<< hash(v);
             dlog << LINFO << "hash(m): "<< hash(m);
+            dlog << LINFO << "hash(mat): "<< hash(mat);
 
             DLIB_TEST(hash(str1) == 1073638390);
             DLIB_TEST(hash(str2) == 2413364589);
             DLIB_TEST(hash(v) == 4054789286);
             DLIB_TEST(hash(m) == 2865512303);
+            DLIB_TEST(hash(mat) == 1043635621);
             DLIB_TEST(murmur_hash3(&str1[0], str1.size(), 0) == 1073638390);
 
             dlog << LINFO << "hash(str1,1): "<< hash(str1,1);
             dlog << LINFO << "hash(str2,2): "<< hash(str2,2);
             dlog << LINFO << "hash(v,3): "<< hash(v,3);
-            dlog << LINFO << "hash(m,3): "<< hash(m,4);
+            dlog << LINFO << "hash(m,4): "<< hash(m,4);
+            dlog << LINFO << "hash(mat,5): "<< hash(mat,5);
 
             DLIB_TEST(hash(str1,1) == 2977753747);
             DLIB_TEST(hash(str2,2) == 3656927287);
             DLIB_TEST(hash(v,3) == 2127112268);
             DLIB_TEST(hash(m,4) == 4200495810);
+            DLIB_TEST(hash(mat,5) == 2380427865);
             DLIB_TEST(murmur_hash3(&str1[0], str1.size(), 1) == 2977753747);
 
         }