- Made the random number generator serializable

- Fixed a bug in the random number generator where setting the seed back to ""
   didn't result in the object going back to it's initial state.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403746

dlib/rand/mersenne_twister.h

@@ -96,6 +96,24 @@ namespace dlib
 
             result_type operator()();
 
+            friend void serialize(
+                const mersenne_twister& item, 
+                std::ostream& out
+            )
+            {
+                serialize(item.x, out);
+                serialize(item.i, out);
+            }
+
+            friend void deserialize(
+                mersenne_twister& item, 
+                std::istream& in 
+            )
+            {
+                deserialize(item.x, in);
+                deserialize(item.i, in);
+            }
+
         private:
 
             void twist(int block);

dlib/rand/rand_kernel_1.h

@@ -8,6 +8,8 @@
 #include "rand_kernel_abstract.h"
 #include "mersenne_twister.h"
 #include "../is_kind.h"
+#include <iostream>
+#include "../serialize.h"
 
 namespace dlib
 {
@@ -61,12 +63,23 @@ namespace dlib
             )
             {
                 seed = value;
-                uint32 s = 0;
-                for (std::string::size_type i = 0; i < seed.size(); ++i)
+
+                // make sure we do the seeding so that using a seed of "" gives the same
+                // state as calling this->clear()
+                if (value.size() != 0)
                 {
-                    s = (s*37) + static_cast<uint32>(seed[i]);
+                    uint32 s = 0;
+                    for (std::string::size_type i = 0; i < seed.size(); ++i)
+                    {
+                        s = (s*37) + static_cast<uint32>(seed[i]);
+                    }
+                    mt.seed(s);
                 }
-                mt.seed(s);
+                else
+                {
+                    mt.seed();
+                }
+
                 // prime the generator a bit
                 for (int i = 0; i < 10000; ++i)
                     mt();
@@ -98,6 +111,23 @@ namespace dlib
                 exchange(seed, item.seed);
             }
     
+            friend void serialize(
+                const rand_kernel_1& item, 
+                std::ostream& out
+            )
+            {
+                serialize(item.mt, out);
+                serialize(item.seed, out);
+            }
+
+            friend void deserialize(
+                rand_kernel_1& item, 
+                std::istream& in 
+            )
+            {
+                deserialize(item.mt, in);
+                deserialize(item.seed, in);
+            }
 
         private:
             mt19937 mt;

dlib/test/rand.cpp

@@ -153,6 +153,50 @@ namespace
         sout.str("");
 
 
+        // make sure the things can serialize right
+        {
+            r.clear();
+            r2.clear();
+
+
+            for (int i =0; i < 1000; ++i)
+                r.get_random_32bit_number();
+
+            ostringstream sout;
+            serialize(r, sout);
+
+            istringstream sin(sout.str());
+            deserialize(r2, sin);
+
+
+            for (int i =0; i < 1000; ++i)
+            {
+                DLIB_TEST(r.get_random_32bit_number() == r2.get_random_32bit_number());
+            }
+        }
+
+
+        // make sure calling clear() and set_seed("") do the same thing
+        {
+            r.clear();
+            r2.set_seed("");
+            rand r3;
+
+
+            DLIB_TEST(r.get_seed() == r2.get_seed());
+            DLIB_TEST(r.get_seed() == r3.get_seed());
+
+
+            for (int i =0; i < 1000; ++i)
+            {
+                const uint32 num1 = r.get_random_32bit_number();
+                const uint32 num2 = r2.get_random_32bit_number();
+                const uint32 num3 = r3.get_random_32bit_number();
+                DLIB_TEST( num1 == num2);
+                DLIB_TEST( num1 == num3);
+            }
+        }
+
     }