PCG random number generator

cmake/ExternalTools.cmake

@@ -1,6 +1,24 @@
 include(ExternalProject)
 include(FetchContent)
 
+#############
+# PCG RANDOM
+#############
+
+option(ENABLE_PCG "Enable PCG random number generator" off)
+if (ENABLE_PCG)
+    FetchContent_Declare(
+        pcg-cpp
+        URL https://github.com/imneme/pcg-cpp/archive/ffd522e7188bef30a00c74dc7eb9de5faff90092.tar.gz
+        URL_HASH MD5=051b969bbaf924f35f2159813f93e341)
+    FetchContent_GetProperties(pcg-cpp)
+    if(NOT pcg-cpp_POPULATED)
+        FetchContent_Populate(pcg-cpp)
+    endif()
+    include_directories(SYSTEM ${pcg-cpp_SOURCE_DIR}/include)
+    add_definitions("-DENABLE_PCG")
+endif()
+
 #########
 # EXPRTK 
 #########

docs/_docs/install.md

@@ -74,6 +74,7 @@ CMake Option                         | Description
 `-DENABLE_PYTHON=OFF`                | Build python bindings (experimental)
 `-DENABLE_FREESASA=ON`               | Enable SASA routines (external download)
 `-DENABLE_TBB=OFF`                   | Build with Intel Threading Building Blocks (experimental)
+`-DENABLE_PCG=OFF`                   | Use PCG random number generator instead of C++'s Mersenne Twister
 `-DBUILD_STATIC=OFF`                 | Build statically linked binaries
 `-DCMAKE_BUILD_TYPE=Release`         | Alternatives: `Debug` or `RelWithDebInfo`
 `-DCMAKE_CXX_FLAGS_RELEASE="..."`    | Compiler options for Release mode

examples/cluster-ideal/cluster-ideal.yml

@@ -5,7 +5,7 @@
 #     N_c = 1 + 4 * pi * Rc**3 * N / (3 * L**3) = 1.22 in this case
 #
 temperature: 300
-random: {seed: fixed}
+random: {seed: hardware}
 geometry: {type: cuboid, length: 40}
 mcloop: {macro: 10, micro: 20000}
 

src/core.cpp

@@ -212,7 +212,7 @@ Point ranunit(Random &rand, const Point &dir) {
 
 TEST_CASE("[Faunus] ranunit") {
     Random r;
-    int n = 2e5;
+    int n = 4e5;
     Point rtp(0, 0, 0);
     for (int i = 0; i < n; i++)
         rtp += xyz2rtp(ranunit(r));

src/random.cpp

@@ -31,9 +31,14 @@ void to_json(nlohmann::json &j, const Random &random) {
     std::ostringstream stream;
     stream << random.engine; // dump engine state to stream
     j["seed"] = stream.str();
+    if constexpr (std::is_same<RandomNumberEngine, std::mt19937>::value) {
+        j["engine"] = "Mersenne Twister (std::mt19937)";
+    } else {
+        j["engine"] = "Permuted Congruential Generator (pcg32)";
+    }
 }
 
-void Random::seed() { engine = std::mt19937(std::random_device()()); }
+void Random::seed() { engine = RandomNumberEngine(std::random_device()()); }
 
 Random::Random() : dist01(0, 1) {}
 

src/random.h

@@ -5,8 +5,19 @@
 #include <stdexcept>
 #include <nlohmann/json_fwd.hpp>
 
+#ifdef ENABLE_PCG
+#include "pcg_random.hpp"
+#endif
+
 namespace Faunus {
 
+#ifdef ENABLE_PCG
+using RandomNumberEngine = pcg32;
+#else
+using RandomNumberEngine = std::mt19937;
+#endif
+
+
 /**
  * @brief Random number generator
  *
@@ -22,7 +33,7 @@ class Random {
   private:
     std::uniform_real_distribution<double> dist01; //!< Uniform real distribution [0,1)
   public:
-    std::mt19937 engine; //!< Random number engine used for all operations
+    RandomNumberEngine engine; //!< Random number engine used for all operations
     Random();            //!< Constructor with deterministic seed
     void seed();         //!< Set a non-deterministic ("hardware") seed
     double operator()(); //!< Random double in uniform range [0,1)