Optimized ShrinkingDistance.combine(..)

Working towards #435 effects

api/src/main/java/net/jqwik/api/ShrinkingDistance.java

@@ -40,12 +40,12 @@ public static <T> ShrinkingDistance combine(List<Shrinkable<T>> shrinkables) {
 		if (shrinkables.isEmpty()) {
 			throw new IllegalArgumentException("At least one shrinkable is required");
 		}
-		ShrinkingDistance acc = new ShrinkingDistance(new long[0]);
-		for (Shrinkable<T> shrinkable : shrinkables) {
-			ShrinkingDistance distance = shrinkable.distance();
-			acc = acc.append(distance);
-		}
-		return acc;
+		// This is an optimization to avoid creating many temporary arrays, which the old streams-based implementation did.
+		List<long[]> shrinkableDistances = shrinkables.stream()
+													  .map(tShrinkable -> tShrinkable.distance().distances)
+													  .collect(Collectors.toList());
+		long[] combinedDistances = concatenate(shrinkableDistances);
+		return new ShrinkingDistance(combinedDistances);
 	}
 
 	private ShrinkingDistance(long[] distances) {
@@ -110,13 +110,13 @@ private int compareDimension(ShrinkingDistance other, int i) {
 
 	@API(status = INTERNAL)
 	public ShrinkingDistance plus(ShrinkingDistance other) {
-		long[] summedUpDistances = sumUpArrays(distances, other.distances);
+		long[] summedUpDistances = sumUp(distances, other.distances);
 		return new ShrinkingDistance(summedUpDistances);
 	}
 
 	@API(status = INTERNAL)
 	public ShrinkingDistance append(ShrinkingDistance other) {
-		long[] appendedDistances = concatArrays(distances, other.distances);
+		long[] appendedDistances = concatenate(Arrays.asList(distances, other.distances));
 		return new ShrinkingDistance(appendedDistances);
 	}
 

api/src/main/java/net/jqwik/api/support/LongArraysSupport.java

@@ -13,7 +13,7 @@ public static long at(long[] array, int i) {
 		return array.length > i ? array[i] : 0;
 	}
 
-	public static long[] sumUpArrays(long[] left, long[] right) {
+	public static long[] sumUp(long[] left, long[] right) {
 		long[] sum = new long[Math.max(left.length, right.length)];
 		for (int i = 0; i < sum.length; i++) {
 			long summedValue = at(left, i) + at(right, i);
@@ -25,9 +25,14 @@ public static long[] sumUpArrays(long[] left, long[] right) {
 		return sum;
 	}
 
-	public static long[] concatArrays(long[] left, long[] right) {
-		long[] concatenated = Arrays.copyOf(left, left.length + right.length);
-		System.arraycopy(right, 0, concatenated, left.length, right.length);
-		return concatenated;
+	public static long[] concatenate(List<long[]> listOfArrays) {
+		int size = listOfArrays.stream().mapToInt(s -> s.length).sum();
+		long[] concatenatedArrays = new long[size];
+		int i = 0;
+		for (long[] array : listOfArrays) {
+			System.arraycopy(array, 0, concatenatedArrays, i, array.length);
+			i += array.length;
+		}
+		return concatenatedArrays;
 	}
 }