Initial implementation of a random number generator class.

src/random.cpp

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+///\file
+
+/******************************************************************************
+The MIT License(MIT)
+
+Embedded Template Library.
+https://github.com/ETLCPP/etl
+http://www.etlcpp.com
+
+Copyright(c) 2017 jwellbelove
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files(the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and / or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions :
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+******************************************************************************/
+
+#include "random.h"
+
+namespace
+{
+  enum
+  {
+      W = 32
+      N = 624,
+      M = 397,
+      R = 31,
+      A = 0x9908B0DF,
+      F = 1812433253,
+      U = 11,
+      S = 7,
+      B = 0x9D2C5680,
+      T = 15,
+      C = 0xEFC60000,
+      L = 18,
+
+      MASK_LOWER = (1ull << R) - 1,
+      MASK_UPPER = (1ull << R)
+  };
+}
+
+namespace etl
+{
+  //***************************************************************************
+  /// Default constructor.
+  //***************************************************************************
+  random::random()
+  {
+    // An attempt to come up with a reasonable non-zero seed.
+    uintptr_t n = reinterpret_cast<uintptr_t>(this);
+    uint32_t seed = static_cast<uint32_t>(n);
+    initialise(seed);
+  }
+
+  //***************************************************************************
+  /// Constructor with seed value.
+  //***************************************************************************
+  random::random(uint32_t seed)
+  {
+    initialise(seed);
+  }
+
+  //***************************************************************************
+  /// Get the next random number.
+  //***************************************************************************
+  uint32_t random::get() const
+  {
+    uint32_t n;
+    uint16_t i = index;
+
+    if (index >= N)
+    {
+      twist();
+      i = index;
+    }
+
+    n = mt[i];
+    index = i + 1;
+
+    n ^= (mt[i] >> U);
+    n ^= (n << S) & B;
+    n ^= (n << T) & C;
+    n ^= (n >> L);
+
+    return n;
+  }
+
+  //***************************************************************************
+  /// Initialises the sequence with a new seed value.
+  //***************************************************************************
+  void random::initialize(uint32_t seed)
+  {
+    uint32_t i;
+
+    mt[0] = seed;
+
+    for (i = 1; i < N; i++)
+    {
+      mt[i] = (F * (mt[i - 1] ^ (mt[i - 1] >> (W - 2))) + i);
+    }
+
+    index = N;
+  }
+
+  //***************************************************************************
+  /// Creates the next iteration.
+  //***************************************************************************
+  void random::twist()
+  {
+    for (uint32_t i = 0; i < N; i++ )
+    {
+      uint32_t x = (mt[i] & MASK_UPPER) + (mt[(i + 1) % N] & MASK_LOWER);
+
+      uint32_t xA = x >> 1;
+
+      if (x & 0x01)
+      {
+        xA ^= A;
+      }
+
+      mt[i] = mt[(i + M) % N] ^ xA;
+    }
+
+    index = 0;
+  }
+}

src/random.h

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+
+#ifndef __ETL_RANDOM_INCLUDED_
+#define __ETL_RANDOM_INCLUDED_
+
+#include <stdint.h>
+
+namespace etl
+{
+  //***************************************************************************
+  /// A 32 bit Mersenne Twister random number generator.
+  /// Based on C/C++ code on Wikipedia.
+  /// https://en.wikipedia.org/wiki/Mersenne_Twister#C.2FC.2B.2B_implementation
+  //***************************************************************************
+  class random
+  {
+    public:
+
+      random();
+      random(uint32_t seed);
+      void initialise(uint32_t seed);
+      uint32_t get() const;
+
+  private:
+
+    void twist();
+
+    uint32_t  mt[N];
+    uint16_t  index;
+  };
+}
+
+#endif