base: Use STL C++11 random number generation

This patch changes the random number generator from the in-house
Mersenne twister to an implementation relying entirely on C++11 STL.

The format for the checkpointing of the twister is simplified. As the
functionality was never used this should not matter. Note that this
patch does not actually make use of the checkpointing
functionality. As the random number generator is not thread safe, it
may be sensible to create one generator per thread, system, or even
object. Until this is decided the status quo is maintained in that no
generator state is part of the checkpoint.

1 files changed, 39 insertions, 169 deletions

diff --git a/src/base/random.hh b/src/base/random.hh
index 34107c76f..cedbd6bd4 100644
--- a/src/base/random.hh
+++ b/src/base/random.hh
@@ -1,4 +1,16 @@
 /*
+ * Copyright (c) 2014 ARM Limited
+ * All rights reserved
+ *
+ * The license below extends only to copyright in the software and shall
+ * not be construed as granting a license to any other intellectual
+ * property including but not limited to intellectual property relating
+ * to a hardware implementation of the functionality of the software
+ * licensed hereunder.  You may use the software subject to the license
+ * terms below provided that you ensure that this notice is replicated
+ * unmodified and in its entirety in all distributions of the software,
+ * modified or unmodified, in source code or in binary form.
+ *
  * Copyright (c) 2003-2005 The Regents of The University of Michigan
  * All rights reserved.
  *
@@ -27,20 +39,19 @@
  *
  * Authors: Nathan Binkert
  *          Ali Saidi
+ *          Andreas Hansson
  */
 
 /*
- * Mersenne Twister random number generator has a period of
- * 2^19937-1.
- *
- * The actual math is in its own file to keep the license clear.
+ * Mersenne twister random number generator.
  */
 
 #ifndef __BASE_RANDOM_HH__
 #define __BASE_RANDOM_HH__
 
-#include <ios>
+#include <random>
 #include <string>
+#include <type_traits>
 
 #include "base/types.hh"
 
@@ -48,192 +59,51 @@ class Checkpoint;
 
 class Random
 {
-  protected:
-    static const int N = 624;
-    static const int M = 397;
-    static const uint32_t MATRIX_A = (uint32_t)0x9908b0df;
-    static const uint32_t UPPER_MASK = (uint32_t)0x80000000;
-    static const uint32_t LOWER_MASK = (uint32_t)0x7fffffff;
-
-    uint32_t mt[N];
-    int mti;
-
-    uint32_t genrand();
-    uint32_t genrand(uint32_t max);
-    uint64_t genrand(uint64_t max);
-
-    void
-    _random(int8_t &value)
-    {
-        value = genrand() & (int8_t)-1;
-    }
-
-    void
-    _random(int16_t &value)
-    {
-        value = genrand() & (int16_t)-1;
-    }
-
-    void
-    _random(int32_t &value)
-    {
-        value = (int32_t)genrand();
-    }
-
-    void
-    _random(int64_t &value)
-    {
-        value = (int64_t)genrand() << 32 | (int64_t)genrand();
-    }
-
-    void
-    _random(uint8_t &value)
-    {
-        value = genrand() & (uint8_t)-1;
-    }
 
-    void
-    _random(uint16_t &value)
-    {
-        value = genrand() & (uint16_t)-1;
-    }
-
-    void
-    _random(uint32_t &value)
-    {
-        value = genrand();
-    }
+  private:
 
-    void
-    _random(uint64_t &value)
-    {
-        value = (uint64_t)genrand() << 32 | (uint64_t)genrand();
-    }
-
-    // [0,1]
-    void
-    _random(float &value)
-    {
-        // ieee floats have 23 bits of mantissa
-        value = (genrand() >> 9) / 8388608.0;
-    }
-
-    // [0,1]
-    void
-    _random(double &value)
-    {
-        double number = genrand() * 2097152.0 + (genrand() >> 11);
-        value = number / 9007199254740992.0;
-    }
-
-
-    // Range based versions of the random number generator
-    int8_t
-    _random(int8_t min, int8_t max)
-    {
-        uint32_t diff = max - min;
-        return static_cast<int8_t>(min + genrand(diff));
-    }
-
-    int16_t
-    _random(int16_t min, int16_t max)
-    {
-        uint32_t diff = max - min;
-        return static_cast<int16_t>(min + genrand(diff));
-    }
-
-    int32_t
-    _random(int32_t min, int32_t max)
-    {
-        uint32_t diff = max - min;
-        return static_cast<int32_t>(min + genrand(diff));
-    }
-
-    int64_t
-    _random(int64_t min, int64_t max)
-    {
-        uint64_t diff = max - min;
-        return static_cast<int64_t>(min + genrand(diff));
-    }
-
-    uint8_t
-    _random(uint8_t min, uint8_t max)
-    {
-        uint32_t diff = max - min;
-        return static_cast<uint8_t>(min + genrand(diff));
-    }
-
-    uint16_t
-    _random(uint16_t min, uint16_t max)
-    {
-        uint32_t diff = max - min;
-        return static_cast<uint16_t>(min + genrand(diff));
-    }
-
-    uint32_t
-    _random(uint32_t min, uint32_t max)
-    {
-        uint32_t diff = max - min;
-        return static_cast<uint32_t>(min + genrand(diff));
-    }
-
-    uint64_t
-    _random(uint64_t min, uint64_t max)
-    {
-        uint64_t diff = max - min;
-        return static_cast<uint64_t>(min + genrand(diff));
-    }
+    std::mt19937_64 gen;
 
   public:
+
     Random();
     Random(uint32_t s);
-    Random(uint32_t init_key[], int key_length);
     ~Random();
 
     void init(uint32_t s);
-    void init(uint32_t init_key[], int key_length);
 
+    /**
+     * Use the SFINAE idiom to choose an implementation based on
+     * whether the type is integral or floating point.
+     */
     template <typename T>
-    T
+    typename std::enable_if<std::is_integral<T>::value, T>::type
     random()
     {
-        T value;
-        _random(value);
-        return value;
+        // [0, max_value] for integer types
+        std::uniform_int_distribution<T> dist;
+        return dist(gen);
     }
 
     template <typename T>
-    T
-    random(T min, T max)
-    {
-        return _random(min, max);
-    }
-
-    // [0,1]
-    double
-    gen_real1()
-    {
-        return genrand() / 4294967296.0;
-    }
-
-    // [0,1)
-    double
-    gen_real2()
+    typename std::enable_if<std::is_floating_point<T>::value, T>::type
+    random()
     {
-        return genrand() / 4294967295.0;
+        // [0, 1) for real types
+        std::uniform_real_distribution<T> dist;
+        return dist(gen);
     }
 
-    // (0,1)
-    double
-    gen_real3()
+    template <typename T>
+    typename std::enable_if<std::is_integral<T>::value, T>::type
+    random(T min, T max)
     {
-        return ((double)genrand() + 0.5) / 4294967296.0;
+        std::uniform_int_distribution<T> dist(min, max);
+        return dist(gen);
     }
 
-  public:
-    void serialize(const std::string &base, std::ostream &os);
-    void unserialize(const std::string &base, Checkpoint *cp,
-                     const std::string &section);
+    void serialize(std::ostream &os);
+    void unserialize(Checkpoint *cp, const std::string &section);
 };
 
 extern Random random_mt;