extract functionality

Author: mtf90

commons/util/src/main/java/module-info.java

@@ -45,6 +45,7 @@
     exports net.automatalib.common.util.io;
     exports net.automatalib.common.util.lib;
     exports net.automatalib.common.util.mapping;
+    exports net.automatalib.common.util.math;
     exports net.automatalib.common.util.nid;
     exports net.automatalib.common.util.process;
     exports net.automatalib.common.util.random;

commons/util/src/main/java/net/automatalib/common/util/math/MathUtil.java

@@ -0,0 +1,73 @@
+/* Copyright (C) 2013-2024 TU Dortmund University
+ * This file is part of AutomataLib, http://www.automatalib.net/.
+ *
+ * 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.
+ */
+package net.automatalib.common.util.math;
+
+/**
+ * Utility class for mathematical computations.
+ */
+public final class MathUtil {
+
+    private MathUtil() {
+        // prevent instantiation
+    }
+
+    /**
+     * Computes the binomial coefficient n over k using Pascal's triangle. If the binomial coefficient exceeds the
+     * maximum number representable by a long, this methods returns {@link Long#MAX_VALUE} instead.
+     *
+     * @param n
+     *         the value for n
+     * @param k
+     *         the value for k
+     *
+     * @return the binomial coefficient n over k
+     */
+    public static long binomial(int n, int k) {
+
+        if (k < 0 || n < k) {
+            throw new IllegalArgumentException("Illegal values for n and k");
+        }
+
+        // abuse symmetry
+        final int effectiveK = Math.min(k, n - k);
+
+        // pascal's triangle using a one dimensional storage
+        final int dimN = n + 1;
+        final int dimK = effectiveK + 1;
+        final long[] tmp = new long[dimN * dimK];
+
+        try {
+            for (int i = 0; i <= n; i++) {
+                final int min = Math.min(i, effectiveK);
+                for (int j = 0; j <= min; j++) {
+                    if (j == 0 || j == i) {
+                        // tmp[i][j] = 1
+                        tmp[i * dimK + j] = 1;
+                    } else {
+                        // tmp[i][j] = tmp[i-1][j-1] + tmp[i-1][k]
+                        tmp[i * dimK + j] = Math.addExact(tmp[(i - 1) * dimK + j - 1], tmp[(i - 1) * dimK + j]);
+                    }
+                }
+            }
+
+            // tmp[n][k]
+            return tmp[n * dimK + effectiveK];
+        } catch (ArithmeticException ae) {
+            return Long.MAX_VALUE;
+        }
+    }
+
+}

commons/util/src/test/java/net/automatalib/common/util/math/MathUtilTest.java

@@ -0,0 +1,36 @@
+/* Copyright (C) 2013-2024 TU Dortmund University
+ * This file is part of AutomataLib, http://www.automatalib.net/.
+ *
+ * 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.
+ */
+package net.automatalib.common.util.math;
+
+import org.testng.Assert;
+import org.testng.annotations.Test;
+
+public class MathUtilTest {
+
+    @Test
+    public void testBinom() {
+        Assert.assertThrows(IllegalArgumentException.class, () -> MathUtil.binomial(5, -1));
+        Assert.assertEquals(MathUtil.binomial(5, 0), 1);
+        Assert.assertEquals(MathUtil.binomial(5, 1), 5);
+        Assert.assertEquals(MathUtil.binomial(5, 2), 10);
+        Assert.assertEquals(MathUtil.binomial(5, 3), 10);
+        Assert.assertEquals(MathUtil.binomial(5, 4), 5);
+        Assert.assertEquals(MathUtil.binomial(5, 5), 1);
+        Assert.assertThrows(IllegalArgumentException.class, () -> MathUtil.binomial(5, 6));
+
+        Assert.assertEquals(MathUtil.binomial(70, 35), Long.MAX_VALUE);
+    }
+}

util/src/main/java/net/automatalib/util/automaton/ads/ADSUtil.java

@@ -22,6 +22,7 @@
 
 import net.automatalib.automaton.transducer.MealyMachine;
 import net.automatalib.common.util.Pair;
+import net.automatalib.common.util.math.MathUtil;
 import net.automatalib.graph.ads.ADSNode;
 import net.automatalib.graph.ads.impl.ADSSymbolNode;
 import net.automatalib.word.Word;
@@ -149,34 +150,6 @@ public static long computeMaximumSplittingWordLength(int n, int i, int m) {
             return n;
         }
 
-        return binomial(n, i) - binomial(m - 1, i - 1) - 1;
+        return MathUtil.binomial(n, i) - MathUtil.binomial(m - 1, i - 1) - 1;
     }
-
-    private static long binomial(int n, int k) {
-
-        // abuse symmetry
-        final int effectiveK = Math.min(k, n - k);
-
-        // pascal's triangle using a one dimensional storage
-        final int dimN = n + 1;
-        final int dimK = effectiveK + 1;
-        final long[] tmp = new long[dimN * dimK];
-
-        for (int i = 0; i <= n; i++) {
-            final int min = Math.min(i, effectiveK);
-            for (int j = 0; j <= min; j++) {
-                if (j == 0 || j == i) {
-                    // tmp[i][j] = 1
-                    tmp[i * dimK + j] = 1;
-                } else {
-                    // tmp[i][j] = tmp[i-1][j-1] + tmp[i-1][k]
-                    tmp[i * dimK + j] = tmp[(i - 1) * dimK + j - 1] + tmp[(i - 1) * dimK + j];
-                }
-            }
-        }
-
-        // tmp[n][k]
-        return tmp[n * dimK + effectiveK];
-    }
-
 }