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//@HEADER
// ************************************************************************
//
// Kokkos v. 4.0
// Copyright (2022) National Technology & Engineering
// Solutions of Sandia, LLC (NTESS).
//
// Under the terms of Contract DE-NA0003525 with NTESS,
// the U.S. Government retains certain rights in this software.
//
// Part of Kokkos, under the Apache License v2.0 with LLVM Exceptions.
// See https://kokkos.org/LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//@HEADER
#include <Kokkos_Core.hpp>
#include <cstdio>
#include <cstdlib>
#include <cmath>
// Type of a one-dimensional length-N array of int.
using view_type = Kokkos::View<int*>;
using host_view_type = view_type::HostMirror;
// 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.
using count_type = Kokkos::View<int>;
using host_count_type = count_type::HostMirror;
// 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 = std::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);
using size_type = view_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 < static_cast<size_type>(data.extent(0)); ++i) {
h_data(i) = rand() % nnumbers;
}
Kokkos::deep_copy(data, h_data); // copy from host to device
Kokkos::parallel_for(data.extent(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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