benchmark: reproducible random lists

app/src/jmh/java/de/uni_marburg/powersort/benchmark/MainJmh.java

@@ -46,11 +46,15 @@ public class MainJmh {
     // TODO: This is inaccurate. How to create and use separate arrays for each warmup x iteration x sortAlgorithm ?
     @Setup(Level.Invocation)
     public void setup() {
-        // TODO: We tried to store the old `dataEnum` in a separate variable and only call `dataEnum.get()` if `dataEnum` changed. But the separate variable was always reverted to `null`. Why? Maybe as the benchmark method does not use it?
+        // A new MainJmh object is created for each @Param variation.
-        // TODO: This leads to different random lists used for each sort impl.
+        // Then, `data` is `null` again.
-        //
+        if (data == null) {
-        // TODO: This is better anyways: Store random list on disk and reuse it for reproducibility
             data = dataEnum.get();
+        }
+        // For all warmup and measurement iterations of one @Param variation, the MainJmh object is reused.
+        // Thus, we can't just sort `data` directly.
+        // Instead, we have to create a copy of it on which the sort algorithm can work.
+        // This way, all iterations sort the same input.
         workingCopy = data.getCopy();
     }
 

app/src/main/java/de/uni_marburg/powersort/benchmark/IntegerArray.java

@@ -4,14 +4,10 @@ public class IntegerArray {
     private IntegerArray() {
     }
 
-    public static Integer[] random(final int length) {
+    public static Integer[] random(final int length, final long seed) {
-        return random(length, Integer.MIN_VALUE, Integer.MAX_VALUE);
-    }
-
-    public static Integer[] random(final int length, final int minInt, final int maxInt) {
         final Integer[] list = new Integer[length];
         for (int i = 0; i < length; i++) {
-            list[i] = RandomInt.integer(minInt, maxInt);
+            list[i] = RandomInt.integer(seed);
         }
         return list;
     }

app/src/main/java/de/uni_marburg/powersort/benchmark/RandomInt.java

@@ -1,5 +1,7 @@
 package de.uni_marburg.powersort.benchmark;
 
+import java.util.Random;
+
 /**
  * Provides utility methods related to random integers.
  */
@@ -8,15 +10,33 @@ public final class RandomInt {
   }
 
   /**
-   * Returns a random integer.
-   *
    * @return A random integer.
    */
   public static int integer() {
     return integer(Integer.MIN_VALUE, Integer.MAX_VALUE);
   }
   public static int integer(final int minInt, final int maxInt) {
-    final double random = Math.random() * (maxInt - minInt) - minInt;
+    final double rand01 = Math.random();
-    return (int) Math.round(random);
+    return helper(minInt, maxInt, rand01);
+  }
+
+  /**
+   * The returned random integer to return is determined by the given seed.
+   *
+   * @return A random integer.
+   */
+  public static int integer(final long seed) {
+    Random random = new Random(seed);
+    final double rand01 = random.nextDouble();
+    return helper(Integer.MIN_VALUE, Integer.MAX_VALUE, rand01);
+
+  }
+
+  /**
+   * @param rand01 Random value in range [0,1)
+   */
+  private static int helper(final int minInt, final int maxInt, final double rand01) {
+    final double randMinMax = rand01 * (maxInt - minInt) - minInt;
+    return (int) Math.round(randMinMax);
   }
 }

app/src/main/java/de/uni_marburg/powersort/data/DataEnum.java

@@ -6,8 +6,12 @@ public enum DataEnum {
     DESCENDING_INTEGERS;
 
     public ObjectSupplier get() {
+        // We use a seed to get the same random list every time -> Repeatable benchmarks on same input data!
+        // final long seed = 3651660232967549736L; // System.nanoTime() ++ Math.random()
+        final long seed = 140506881906827520L; // (long) 'P' * (long) 'O' *(long) 'W' * (long) 'E' * (long) 'R' * (long) 'S' * (long) 'O' * (long) 'R' * (long) 'T';
+
         return switch (this) {
-            case RANDOM_INTEGERS -> new RandomIntegers();
+            case RANDOM_INTEGERS -> new RandomIntegers(seed);
             case ASCENDING_INTEGERS -> new AscendingIntegers();
             case DESCENDING_INTEGERS -> new DescendingIntegers();
         };

app/src/main/java/de/uni_marburg/powersort/data/RandomIntegers.java

@@ -6,8 +6,8 @@ import de.uni_marburg.powersort.benchmark.LongFormatter;
 import static de.uni_marburg.powersort.data.DataArraySizes.SIZE_RAND;
 
 public class RandomIntegers extends IntegerSupplier {
-    public RandomIntegers() {
+    public RandomIntegers(final long seed) {
-        super(IntegerArray.random(SIZE_RAND));
+        super(IntegerArray.random(SIZE_RAND, seed));
     }
 
     @Override

app/src/test/java/de/uni_marburg/powersort/benchmark/RandomIntTest.java

@@ -3,6 +3,8 @@ package de.uni_marburg.powersort.benchmark;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
 class RandomIntTest {
     protected RandomIntTest() {
         // This constructor is intentionally empty. Nothing special is needed here.
@@ -33,4 +35,14 @@ class RandomIntTest {
 
         Assertions.fail("min or max not reached - not a random int generator");
     }
+
+    @Test
+    void testReproducibility() {
+        long seed = 1337;
+
+        int expected = 2147483647;
+        long actual = RandomInt.integer(seed);
+
+        assertEquals(expected, actual);
+    }
 }