added divisors

Author: raphael-s-steiner

include/osp/auxiliary/math/divisors.hpp

@@ -0,0 +1,72 @@
+/*
+Copyright 2025 Huawei Technologies Co., Ltd.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+
+@author Toni Boehnlein, Christos Matzoros, Pal Andras Papp, Raphael S. Steiner
+*/
+#pragma once
+
+#include <cassert>
+#include <cmath>
+#include <limits>
+#include <type_traits>
+#include <vector>
+
+namespace osp {
+
+template<typename integral_type>
+integral_type intSqrtFloor(integral_type num) {
+    static_assert(std::is_integral_v<integral_type>);
+    assert(num > 0);
+
+    integral_type sqrt = 1;
+    integral_type numCopy = num;
+    while (numCopy >= 4) {
+        sqrt *= 2;
+        numCopy /= 4;
+    }
+    integral_type power2 = sqrt / 2;
+    while (power2 > 0) {
+        integral_type sum = sqrt + power2;
+        if (sum * sum <= num) {
+            sqrt = sum;
+        }
+        power2 /= 2;
+    }
+
+    return sqrt;
+}
+
+
+template<typename integral_type>
+std::vector<integral_type> divisorsList(integral_type num) {
+    static_assert(std::is_integral_v<integral_type>);
+    assert(num > 0);
+
+    std::vector<integral_type> divs;
+
+    integral_type ub = intSqrtFloor<integral_type>(num);
+    for (integral_type div = 1; div <= ub; ++div) {
+        if (num % div == 0) {
+            divs.emplace_back(div);
+        }
+    }
+    for (std::size_t indx = divs.back() * divs.back() == num ? divs.size() - 2U : divs.size() - 1U; indx != std::numeric_limits<std::size_t>::max(); --indx) {
+        divs.emplace_back(num / divs[indx]);
+    }
+
+    return divs;
+}
+
+} // end namespace osp

include/osp/auxiliary/math_helper.hpp …clude/osp/auxiliary/math/math_helper.hppinclude/osp/auxiliary/math_helper.hpp renamed to include/osp/auxiliary/math/math_helper.hpp include/osp/auxiliary/math_helper.hpp renamed to include/osp/auxiliary/math/math_helper.hpp

@@ -23,7 +23,7 @@ limitations under the License.
 #include <random>
 #include <vector>
 
-#include "osp/auxiliary/math_helper.hpp"
+#include "osp/auxiliary/math/math_helper.hpp"
 #include "osp/auxiliary/misc.hpp"
 #include "osp/concepts/directed_graph_concept.hpp"
 #include "directed_graph_util.hpp"

include/osp/graph_algorithms/directed_graph_top_sort.hpp

@@ -25,7 +25,7 @@ limitations under the License.
 #include <type_traits>
 #include <vector>
 
-#include "osp/auxiliary/math_helper.hpp"
+#include "osp/auxiliary/math/math_helper.hpp"
 #include "osp/concepts/computational_dag_concept.hpp"
 #include "osp/concepts/directed_graph_edge_desc_concept.hpp"
 #include "osp/concepts/constructable_computational_dag_concept.hpp"

include/osp/graph_implementations/adj_list_impl/compact_sparse_graph.hpp

@@ -93,6 +93,8 @@ _add_test( pebbling_schedule_class )
 ## auxiliary
 _add_test( intpower )
 
+_add_test( divisors )
+
 _add_test( uf_structures )
 
 _add_test( set_operations )

tests/CMakeLists.txt

@@ -0,0 +1,59 @@
+/*
+Copyright 2024 Huawei Technologies Co., Ltd.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+
+@author Toni Boehnlein, Benjamin Lozes, Pal Andras Papp, Raphael S. Steiner
+*/
+
+#define BOOST_TEST_MODULE IntPower
+#include <boost/test/unit_test.hpp>
+
+#include "osp/auxiliary/math/divisors.hpp"
+
+using namespace osp;
+
+BOOST_AUTO_TEST_CASE(IntegerSqrt) {
+    for (std::size_t root = 1U; root < 200U; ++root) {
+        for (std::size_t num = root * root; num < (root + 1U) * (root + 1U); ++num) {
+            BOOST_CHECK_EQUAL(intSqrtFloor(num), root);
+        }
+    }
+
+    for (int root = 1; root < 300; ++root) {
+        for (int num = root * root; num < (root + 1) * (root + 1); ++num) {
+            BOOST_CHECK_EQUAL(intSqrtFloor(num), root);
+        }
+    }
+}
+
+BOOST_AUTO_TEST_CASE(Divisors) {
+    for (std::size_t num = 1U; num < 1000U; ++num) {
+        const std::vector<std::size_t> divs = divisorsList(num);
+        for (const std::size_t &div : divs) {
+            std::cout << div << ", ";
+            BOOST_CHECK_EQUAL(num % div, 0U);
+        }
+        std::cout << "\n";
+        
+        auto it = divs.begin();
+        for (std::size_t i = 1U; i <= num; ++i) {
+            if (num % i == 0) {
+                BOOST_CHECK(it != divs.end());
+                BOOST_CHECK_EQUAL(i, *it);
+                ++it;
+            }
+        }
+        BOOST_CHECK(it == divs.end());
+    }
+}