add pairwise rank first version

utils/xgboost_random.h

@@ -127,6 +127,21 @@ namespace xgboost{
             Shuffle(&data[0], data.size());
         }
     };
+    
+    namespace random{
+        struct Random{
+            /*! \brief set random number seed */
+            inline void Seed( unsigned sd ){
+                this->rseed = sd;
+            }
+            /*! \brief return a real number uniform in [0,1) */
+            inline double RandDouble( void ){
+                return static_cast<double>( rand_r( &rseed ) ) / (static_cast<double>( RAND_MAX )+1.0);
+            }
+            // random number seed
+            unsigned rseed;
+        };
+    };
 };
 
 #endif