ceph/src/boost/libs/compute/example/monte_carlo.cpp

   1 //---------------------------------------------------------------------------//
   2 // Copyright (c) 2013 Kyle Lutz <kyle.r.lutz@gmail.com>
   3 //
   4 // Distributed under the Boost Software License, Version 1.0
   5 // See accompanying file LICENSE_1_0.txt or copy at
   6 // http://www.boost.org/LICENSE_1_0.txt
   7 //
   8 // See http://boostorg.github.com/compute for more information.
   9 //---------------------------------------------------------------------------//
  10
  11 #include <iostream>
  12
  13 #include <boost/compute/function.hpp>
  14 #include <boost/compute/system.hpp>
  15 #include <boost/compute/algorithm/count_if.hpp>
  16 #include <boost/compute/container/vector.hpp>
  17 #include <boost/compute/iterator/buffer_iterator.hpp>
  18 #include <boost/compute/random/default_random_engine.hpp>
  19 #include <boost/compute/types/fundamental.hpp>
  20
  21 namespace compute = boost::compute;
  22
  23 int main()
  24 {
  25     // get default device and setup context
  26     compute::device gpu = compute::system::default_device();
  27     compute::context context(gpu);
  28     compute::command_queue queue(context, gpu);
  29
  30     std::cout << "device: " << gpu.name() << std::endl;
  31
  32     using compute::uint_;
  33     using compute::uint2_;
  34
  35     // ten million random points
  36     size_t n = 10000000;
  37
  38     // generate random numbers
  39     compute::default_random_engine rng(queue);
  40     compute::vector<uint_> vector(n * 2, context);
  41     rng.generate(vector.begin(), vector.end(), queue);
  42
  43     // function returing true if the point is within the unit circle
  44     BOOST_COMPUTE_FUNCTION(bool, is_in_unit_circle, (const uint2_ point),
  45     {
  46         const float x = point.x / (float) UINT_MAX - 1;
  47         const float y = point.y / (float) UINT_MAX - 1;
  48
  49         return (x*x + y*y) < 1.0f;
  50     });
  51
  52     // iterate over vector<uint> as vector<uint2>
  53     compute::buffer_iterator<uint2_> start =
  54         compute::make_buffer_iterator<uint2_>(vector.get_buffer(), 0);
  55     compute::buffer_iterator<uint2_> end =
  56         compute::make_buffer_iterator<uint2_>(vector.get_buffer(), vector.size() / 2);
  57
  58     // count number of random points within the unit circle
  59     size_t count = compute::count_if(start, end, is_in_unit_circle, queue);
  60
  61     // print out values
  62     float count_f = static_cast<float>(count);
  63     std::cout << "count: " << count << " / " << n << std::endl;
  64     std::cout << "ratio: " << count_f / float(n) << std::endl;
  65     std::cout << "pi = " << (count_f / float(n)) * 4.0f << std::endl;
  66
  67     return 0;
  68 }