use mt19937 also in default random generator

previously rng::next_random_impl() returned rand() which is in range
1-2^16. so random_new::generator->next_random() would return a number
1-2^16 in unsynced context and a number in 1-2^32 in synced contexts.
Now it always returns a number in 1-2^32.

src/random_new.cpp

@@ -18,6 +18,8 @@
 
 #include <cassert>
 #include <stdlib.h>
+#include <boost/random/mersenne_twister.hpp>
+#include <time.h>
 
 static lg::log_domain log_random("random");
 #define DBG_RND LOG_STREAM(debug, log_random)
@@ -25,9 +27,29 @@ static lg::log_domain log_random("random");
 #define WRN_RND LOG_STREAM(warn, log_random)
 #define ERR_RND LOG_STREAM(err, log_random)
 
+namespace {
+
+	class rng_default : public random_new::rng
+	{
+	public:
+		rng_default()
+			: gen_(time(NULL))
+		{
+		}
+	protected:
+		virtual uint32_t next_random_impl()
+		{
+			return gen_();
+		}
+	private:
+		boost::mt19937 gen_;
+	};
+}
+
 namespace random_new
 {
-	rng* generator = new rng();
+
+	rng* generator = &rng::default_instance();
 
 	rng::rng()
 		: random_calls_(0)
@@ -40,6 +62,12 @@ namespace random_new
 
 	}
 
+	rng& rng::default_instance()
+	{
+		static rng* def = new rng_default();
+		return *def;
+	}
+
 	unsigned int rng::get_random_calls()
 	{
 		return random_calls_;
@@ -71,13 +99,4 @@ namespace random_new
 		assert(max >= 0);
 		return static_cast<int> (next_random() % (static_cast<uint32_t>(max)+1));
 	}
-
-	uint32_t rng::next_random_impl()
-	{
-		//getting here means random was called form outsiude a synced context.
-		uint32_t retv = rand();
-		
-		LOG_RND << "random_new::rng::next_random returned " << retv;
-		return retv;
-	}
 }

src/random_new.hpp

@@ -49,9 +49,9 @@ namespace random_new
 		 */
 		int get_random_int(int min, int max) 
 		{ return min + get_random_int_in_range_zero_to(max - min); }
-
+		static rng& default_instance();
 	protected:
-		virtual uint32_t next_random_impl();
+		virtual uint32_t next_random_impl() = 0;
 		unsigned int random_calls_;
 
 	private:
@@ -68,6 +68,5 @@ namespace random_new
 		Outside a synced context this has the same effect as rand()
 	*/
 	extern rng* generator;
-
 }
 #endif

src/synced_context.cpp

@@ -503,15 +503,14 @@ int set_scontext_synced::get_random_calls()
 
 
 leave_synced_context::leave_synced_context()
-	: new_rng_()
-	, old_rng_(random_new::generator)
+	: old_rng_(random_new::generator)
 {
 	assert(synced_context::get_synced_state() == synced_context::SYNCED);
 	synced_context::set_synced_state(synced_context::LOCAL_CHOICE);
 
 	//calling the synced rng form inside a local_choice would cause oos.
 	//TODO: should we also reset the synced checkup?
-	random_new::generator = &new_rng_;
+	random_new::generator = &random_new::rng::default_instance();
 }
 
 leave_synced_context::~leave_synced_context()

src/synced_context.hpp

@@ -206,7 +206,6 @@ public:
 	leave_synced_context();
 	~leave_synced_context();
 private:
-	random_new::rng new_rng_;
 	random_new::rng* old_rng_;
 };