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MergeSort.java
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MergeSort.java
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/**
* Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
*
* 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
*
* https://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 org.pkl.core.stdlib.base;
import org.pkl.core.runtime.VmFunction;
import org.pkl.core.stdlib.base.CollectionNodes.SortComparatorNode;
import org.pkl.core.util.Nullable;
final class MergeSort {
// must be a power of two
private static final int INITIAL_MERGE_SORT_STRIDE = 8;
private MergeSort() {}
public static Object[] sort(
Object[] array, SortComparatorNode comparator, @Nullable VmFunction function) {
var length = array.length;
var temp = new Object[length];
// start is inclusive, end is exclusive
for (var start = 0; start < length; start += INITIAL_MERGE_SORT_STRIDE) {
var end = Math.min(start + INITIAL_MERGE_SORT_STRIDE, length);
insertionSort(array, start, end, comparator, function);
}
for (var stride = INITIAL_MERGE_SORT_STRIDE; stride < length; stride *= 2) {
for (var start = 0; start < length - stride; start += stride + stride) {
var end = Math.min(start + stride + stride, length);
var mid = start + stride; // start of second half
merge(array, temp, start, mid, end, comparator, function);
}
}
return array;
}
private static void merge(
Object[] array,
Object[] temp,
int start,
int mid,
int end,
SortComparatorNode comparator,
@Nullable VmFunction function) {
if (comparator.executeWith(array[mid], array[mid], function)) {
return; // already sorted
}
System.arraycopy(array, start, temp, start, end - start);
var i = start;
var j = mid;
for (var k = start; k < end; k++) {
if (i >= mid) array[k] = temp[j++];
else if (j >= end) array[k] = temp[i++];
else if (comparator.executeWith(temp[j], temp[i], function)) array[k] = temp[j++];
else array[k] = temp[i++];
}
}
private static void insertionSort(
Object[] array,
int start,
int end,
SortComparatorNode comparator,
@Nullable VmFunction function) {
for (var i = start; i < end; i++) {
for (var j = i; j > start && comparator.executeWith(array[j], array[j - 1], function); j--) {
Object swap = array[j];
array[j] = array[j - 1];
array[j - 1] = swap;
}
}
}
}