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wrap-host-buffer.cpp

This tutorial shows how ViennaCL can be used to wrap user-provided memory buffers allocated on the host. The benefit of such a wrapper is that the algorithms in ViennaCL can directly be run without pre- or postprocessing the data.

We start with including the required headers:

// System headers
#include <iostream>
#include <cstdlib>
#include <string>
// ViennaCL headers
#include "viennacl/vector.hpp"

We setup two STL-vectors and add them up as a reference. Then the buffer get wrapped by ViennaCL and added up.

int main()
{
typedef float ScalarType;

## Part 1: Allocate some buffers on the host

std::size_t size = 10;
std::vector<ScalarType> host_x(size, 1.0);
std::vector<ScalarType> host_y(size, 2.0);
std::cout << "Result on host: ";
for (std::size_t i=0; i<size; ++i)
std::cout << host_x[i] + host_y[i] << " ";
std::cout << std::endl;

## Part 2: Now do the same computations within ViennaCL

// wrap host buffer within ViennaCL vectors:
viennacl::vector<ScalarType> vcl_vec1(&(host_x[0]), viennacl::MAIN_MEMORY, size); // Second parameter specifies that this is host memory rather than CUDA memory
viennacl::vector<ScalarType> vcl_vec2(&(host_y[0]), viennacl::MAIN_MEMORY, size); // Second parameter specifies that this is host memory rather than CUDA memory
vcl_vec1 += vcl_vec2;
std::cout << "Result with ViennaCL: " << vcl_vec1 << std::endl;
std::cout << "Data in STL-vector: ";
for (std::size_t i=0; i<size; ++i)
std::cout << host_x[i] << " ";
std::cout << std::endl;

That's it. Print success message and exit.

std::cout << "!!!! TUTORIAL COMPLETED SUCCESSFULLY !!!!" << std::endl;
return EXIT_SUCCESS;
}

## Full Example Code

/* =========================================================================
Copyright (c) 2010-2016, Institute for Microelectronics,
Institute for Analysis and Scientific Computing,
TU Wien.
Portions of this software are copyright by UChicago Argonne, LLC.
-----------------
ViennaCL - The Vienna Computing Library
-----------------
Project Head: Karl Rupp rupp@iue.tuwien.ac.at
(A list of authors and contributors can be found in the PDF manual)
License: MIT (X11), see file LICENSE in the base directory
============================================================================= */
// System headers
#include <iostream>
#include <cstdlib>
#include <string>
// ViennaCL headers
#include "viennacl/vector.hpp"
int main()
{
typedef float ScalarType;
std::size_t size = 10;
std::vector<ScalarType> host_x(size, 1.0);
std::vector<ScalarType> host_y(size, 2.0);
std::cout << "Result on host: ";
for (std::size_t i=0; i<size; ++i)
std::cout << host_x[i] + host_y[i] << " ";
std::cout << std::endl;
// wrap host buffer within ViennaCL vectors:
viennacl::vector<ScalarType> vcl_vec1(&(host_x[0]), viennacl::MAIN_MEMORY, size); // Second parameter specifies that this is host memory rather than CUDA memory
viennacl::vector<ScalarType> vcl_vec2(&(host_y[0]), viennacl::MAIN_MEMORY, size); // Second parameter specifies that this is host memory rather than CUDA memory
vcl_vec1 += vcl_vec2;
std::cout << "Result with ViennaCL: " << vcl_vec1 << std::endl;
std::cout << "Data in STL-vector: ";
for (std::size_t i=0; i<size; ++i)
std::cout << host_x[i] << " ";
std::cout << std::endl;
std::cout << "!!!! TUTORIAL COMPLETED SUCCESSFULLY !!!!" << std::endl;
return EXIT_SUCCESS;
}