speed up the random generate

include/LightGBM/utils/random.h

@@ -16,16 +16,17 @@ public:
   /*!
   * \brief Constructor, with random seed
   */
-  Random() 
-    :distribution_zero_to_one_(0.0, 1.0) {
+  Random() {
     std::random_device rd;
-    generator_ = std::mt19937(rd());
+    auto genrator = std::mt19937(rd());
+    std::uniform_int_distribution<int> distribution(0, x);
+    x = static_cast<unsigned int>(distribution(genrator));
   }
   /*!
   * \brief Constructor, with specific seed
   */
-  Random(int seed)
-    :generator_(seed), distribution_zero_to_one_(0.0, 1.0) {
+  Random(int seed) {
+    x = static_cast<unsigned int>(seed);
   }
   /*!
   * \brief Generate random integer
@@ -33,10 +34,8 @@ public:
   * \param upper_bound upper bound
   * \return The random integer between [lower_bound, upper_bound)
   */
-  inline int64_t NextInt(int64_t lower_bound, int64_t upper_bound) {
-    // get random interge in [a,b)
-    std::uniform_int_distribution<int64_t> distribution(lower_bound, upper_bound - 1);
-    return distribution(generator_);
+  inline int NextInt(int lower_bound, int upper_bound) {
+    return (next()) % (upper_bound - lower_bound + 1) + lower_bound;
   }
   /*!
   * \brief Generate random float data
@@ -44,7 +43,7 @@ public:
   */
   inline double NextDouble() {
     // get random float in [0,1)
-    return distribution_zero_to_one_(generator_);
+    return static_cast<double>(next() % 2047) / 2047.0f;
   }
   /*!
   * \brief Sample K data from {0,1,...,N-1}
@@ -66,12 +65,22 @@ public:
     return ret;
   }
 private:
-  /*! \brief Random generator */
-  std::mt19937 generator_;
-  /*! \brief Cache distribution for [0.0, 1.0) */
-  std::uniform_real_distribution<double> distribution_zero_to_one_;
+  unsigned next() {
+    x ^= x << 16;
+    x ^= x >> 5;
+    x ^= x << 1;
+    auto t = x;
+    x = y;
+    y = z;
+    z = t ^ x ^ y;
+    return z;
+  }
+  unsigned int x = 123456789;
+  unsigned int y = 362436069;
+  unsigned int z = 521288629;
 };
 
+
 }  // namespace LightGBM
 
 #endif   // LightGBM_UTILS_RANDOM_H_

include/LightGBM/utils/text_reader.h

@@ -158,7 +158,7 @@ public:
         ++cur_sample_cnt;
       }
       else {
-        const size_t idx = static_cast<size_t>(random.NextInt(0, line_idx + 1));
+        const size_t idx = static_cast<size_t>(random.NextInt(0, static_cast<int>(line_idx + 1)));
         if (idx < static_cast<size_t>(sample_cnt)) {
           out_sampled_data->operator[](idx) = std::string(buffer, size);
         }
@@ -198,7 +198,7 @@ public:
           ++cur_sample_cnt;
         }
         else {
-          const size_t idx = static_cast<size_t>(random.NextInt(0, out_used_data_indices->size()));
+          const size_t idx = static_cast<size_t>(random.NextInt(0, static_cast<int>(out_used_data_indices->size())));
           if (idx < static_cast<size_t>(sample_cnt) ) {
             out_sampled_data->operator[](idx) = std::string(buffer, size);
           }