From e660e5b949b519ae35e043ce3efca8a653f7582d Mon Sep 17 00:00:00 2001
From: John Wellbelove <smartgit@wellbelove.co.uk>
Date: Tue, 8 Aug 2017 18:41:00 +0100
Subject: [PATCH] Added multipy with carry random number generator.

---
 src/random.cpp       | 60 ++++++++++++++++++++++++++++++++++++++++++++
 src/random.h         | 22 ++++++++++++++--
 test/test_random.cpp | 55 +++++++++++++++++++++++++++++++++++++++-
 3 files changed, 134 insertions(+), 3 deletions(-)

diff --git a/src/random.cpp b/src/random.cpp
index c3e5a1c9..7c63d11a 100644
--- a/src/random.cpp
+++ b/src/random.cpp
@@ -288,4 +288,64 @@ namespace etl
 
     return n;
   }
+
+  //***************************************************************************
+  // Multiply with carry random number generator.
+  //***************************************************************************
+
+  //***************************************************************************
+  /// Default constructor.
+  /// Attempts to come up with a unique non-zero seed.
+  //***************************************************************************
+  random_multiply_with_carry::random_multiply_with_carry()
+  {
+    // An attempt to come up with a unique non-zero seed,
+    // based on the address of the instance.
+    uintptr_t n = reinterpret_cast<uintptr_t>(this);
+    uint32_t  seed = static_cast<uint32_t>(n);
+    initialise(seed);
+  }
+
+  //***************************************************************************
+  /// Constructor with seed value.
+  ///\param seed The new seed value.
+  //***************************************************************************
+  random_multiply_with_carry::random_multiply_with_carry(uint32_t seed)
+  {
+    initialise(seed);
+  }
+
+  //***************************************************************************
+  /// Initialises the sequence with a new seed value.
+  ///\param seed The new seed value.
+  //***************************************************************************
+  void random_multiply_with_carry::initialise(uint32_t seed)
+  {
+    value1 = seed;
+    value2 = seed;
+  }
+
+  //***************************************************************************
+  /// Get the next random_lsfr number.
+  //***************************************************************************
+  uint32_t random_multiply_with_carry::operator()()
+  {
+    value1 = 36969 * (value1 & 0xFFFF) + (value1 >> 16);
+    value2 = 18000 * (value2 & 0xFFFF) + (value2 >> 16);
+
+    return (value1 << 16) + value2;
+  }
+
+  //***************************************************************************
+  /// Get the next random_lsfr number in a specified inclusive range.
+  //***************************************************************************
+  uint32_t random_multiply_with_carry::range(uint32_t low, uint32_t high)
+  {
+    uint32_t r = high - low + 1;
+    uint32_t n = operator()();
+    n %= r;
+    n += low;
+
+    return n;
+  }
 }
\ No newline at end of file
diff --git a/src/random.h b/src/random.h
index 5221b41c..1b040fcc 100644
--- a/src/random.h
+++ b/src/random.h
@@ -124,8 +124,6 @@ namespace etl
   //***************************************************************************
   /// A 32 bit random number generator.
   /// Uses a linear shift feedback register.
-  /// Set ITERATIONS_ to control the number of times that the lfsr is iterated on each call.
-  /// Default = 1
   /// https://en.wikipedia.org/wiki/Linear-feedback_shift_register
   //***************************************************************************
   class random_lsfr : public random
@@ -142,6 +140,26 @@ namespace etl
 
       uint32_t value;
   };
+
+  //***************************************************************************
+  /// A 32 bit random number generator.
+  /// Uses a multiply with carry calculation.
+  //***************************************************************************
+  class random_multiply_with_carry : public random
+  {
+  public:
+
+    random_multiply_with_carry();
+    explicit random_multiply_with_carry(uint32_t seed);
+    void initialise(uint32_t seed);
+    uint32_t operator()();
+    uint32_t range(uint32_t low, uint32_t high);
+
+  private:
+
+    uint32_t value1;
+    uint32_t value2;
+  };
 }
 
 #endif
\ No newline at end of file
diff --git a/test/test_random.cpp b/test/test_random.cpp
index cd0038aa..5518a269 100644
--- a/test/test_random.cpp
+++ b/test/test_random.cpp
@@ -238,7 +238,7 @@ namespace
     //=========================================================================
     TEST(test_random_lfsr_range)
     {
-      etl::random_lsfr r(7);
+      etl::random_lsfr r;
 
       uint32_t low  = 1234;
       uint32_t high = 9876;
@@ -251,5 +251,58 @@ namespace
         CHECK(n <= high);
       }
     }
+
+    //=========================================================================
+    TEST(test_random_fast_sequence)
+    {
+      std::vector<uint32_t> out1(10000);
+      etl::random_multiply_with_carry r;
+
+      struct generator
+      {
+        generator(etl::random& r_)
+          : r(r_)
+        {
+        }
+
+        uint32_t operator()()
+        {
+          return r();
+        }
+
+        etl::random& r;
+      };
+
+      std::generate(out1.begin(), out1.end(), generator(r));
+
+      std::ofstream file("random_multiply_with_carry.csv");
+
+      if (!file.fail())
+      {
+        for (size_t i = 0; i < out1.size(); i += 2)
+        {
+          file << out1[i] << "," << out1[i + 1] << "\n";
+        }
+      }
+
+      file.close();
+    }
+
+    //=========================================================================
+    TEST(test_random_fast_range)
+    {
+      etl::random_multiply_with_carry r;
+
+      uint32_t low = 1234;
+      uint32_t high = 9876;
+
+      for (int i = 0; i < 100000; ++i)
+      {
+        uint32_t n = r.range(low, high);
+
+        CHECK(n >= low);
+        CHECK(n <= high);
+      }
+    }
   };
 }