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lammps/lib/kokkos/example/tutorial/05_simple_atomics/simple_atomics.cpp
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/*
//@HEADER
// ************************************************************************
//
// Kokkos v. 2.0
// Copyright (2014) Sandia Corporation
//
// Under the terms of Contract DE-AC04-94AL85000 with Sandia Corporation,
// the U.S. Government retains certain rights in this software.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// 1. Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//
// 2. Redistributions in binary form must reproduce the above copyright
// notice, this list of conditions and the following disclaimer in the
// documentation and/or other materials provided with the distribution.
//
// 3. Neither the name of the Corporation nor the names of the
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY SANDIA CORPORATION "AS IS" AND ANY
// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
// PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL SANDIA CORPORATION OR THE
// CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
// EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
// PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
// NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
// Questions? Contact H. Carter Edwards (hcedwar@sandia.gov)
//
// ************************************************************************
//@HEADER
*/
#include <Kokkos_Core.hpp>
#include <cstdio>
#include <cstdlib>
#include <cmath>
// Type of a one-dimensional length-N array of int.
typedef Kokkos::View<int*> view_type;
typedef view_type::HostMirror host_view_type;
// This is a "zero-dimensional" View, that is, a View of a single
// value (an int, in this case). Access the value using operator()
// with no arguments: e.g., 'count()'.
//
// Zero-dimensional Views are useful for reduction results that stay
// resident in device memory, as well as for irregularly updated
// shared state. We use it for the latter in this example.
typedef Kokkos::View<int> count_type;
typedef count_type::HostMirror host_count_type;
// Functor for finding a list of primes in a given set of numbers. If
// run in parallel, the order of results is nondeterministic, because
// hardware atomic updates do not guarantee an order of execution.
struct findprimes {
view_type data;
view_type result;
count_type count;
findprimes (view_type data_, view_type result_, count_type count_) :
data (data_), result (result_), count (count_)
{}
// Test if data(i) is prime. If it is, increment the count of
// primes (stored in the zero-dimensional View 'count') and add the
// value to the current list of primes 'result'.
KOKKOS_INLINE_FUNCTION
void operator() (const int i) const {
const int number = data(i); // the current number
// Test all numbers from 3 to ceiling(sqrt(data(i))), to see if
// they are factors of data(i). It's not the most efficient prime
// test, but it works.
const int upper_bound = sqrt(1.0*number)+1;
bool is_prime = !(number%2 == 0);
int k = 3;
while (k < upper_bound && is_prime) {
is_prime = !(number%k == 0);
k += 2; // don't have to test even numbers
}
if (is_prime) {
// Use an atomic update both to update the current count of
// primes, and to find a place in the current list of primes for
// the new result.
//
// atomic_fetch_add results the _current_ count, but increments
// it (by 1 in this case). The current count of primes indexes
// into the first unoccupied position of the 'result' array.
const int idx = Kokkos::atomic_fetch_add (&count(), 1);
result(idx) = number;
}
}
};
int main () {
Kokkos::initialize ();
srand (61391); // Set the random seed
int nnumbers = 100000;
view_type data ("RND", nnumbers);
view_type result ("Prime", nnumbers);
count_type count ("Count");
host_view_type h_data = Kokkos::create_mirror_view (data);
host_view_type h_result = Kokkos::create_mirror_view (result);
host_count_type h_count = Kokkos::create_mirror_view (count);
typedef view_type::size_type size_type;
// Fill the 'data' array on the host with random numbers. We assume
// that they come from some process which is only implemented on the
// host, via some library. (That's true in this case.)
for (size_type i = 0; i < data.dimension_0 (); ++i) {
h_data(i) = rand () % nnumbers;
}
Kokkos::deep_copy (data, h_data); // copy from host to device
Kokkos::parallel_for (data.dimension_0 (), findprimes (data, result, count));
Kokkos::deep_copy (h_count, count); // copy from device to host
printf ("Found %i prime numbers in %i random numbers\n", h_count(), nnumbers);
Kokkos::finalize ();
}
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