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/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.apache.hadoop.util;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
/**
* An implementation of the core algorithm of QuickSort.
*/
@InterfaceAudience.Private
@InterfaceStability.Unstable
public final class QuickSort implements IndexedSorter {
private static final IndexedSorter alt = new HeapSort();
public QuickSort() { }
private static void fix(IndexedSortable s, int p, int r) {
if (s.compare(p, r) > 0) {
s.swap(p, r);
}
}
/**
* Deepest recursion before giving up and doing a heapsort.
* Returns 2 * ceil(log(n)).
*/
protected static int getMaxDepth(int x) {
if (x <= 0)
throw new IllegalArgumentException("Undefined for " + x);
return (32 - Integer.numberOfLeadingZeros(x - 1)) << 2;
}
/**
* Sort the given range of items using quick sort.
* {@inheritDoc} If the recursion depth falls below {@link #getMaxDepth},
* then switch to {@link HeapSort}.
*/
@Override
public void sort(IndexedSortable s, int p, int r) {
sort(s, p, r, null);
}
@Override
public void sort(final IndexedSortable s, int p, int r,
final Progressable rep) {
sortInternal(s, p, r, rep, getMaxDepth(r - p));
}
private static void sortInternal(final IndexedSortable s, int p, int r,
final Progressable rep, int depth) {
if (null != rep) {
rep.progress();
}
while (true) {
if (r-p < 13) {
for (int i = p; i < r; ++i) {
for (int j = i; j > p && s.compare(j-1, j) > 0; --j) {
s.swap(j, j-1);
}
}
return;
}
if (--depth < 0) {
// give up
alt.sort(s, p, r, rep);
return;
}
// select, move pivot into first position
fix(s, (p+r) >>> 1, p);
fix(s, (p+r) >>> 1, r - 1);
fix(s, p, r-1);
// Divide
int i = p;
int j = r;
int ll = p;
int rr = r;
int cr;
while(true) {
while (++i < j) {
if ((cr = s.compare(i, p)) > 0) break;
if (0 == cr && ++ll != i) {
s.swap(ll, i);
}
}
while (--j > i) {
if ((cr = s.compare(p, j)) > 0) break;
if (0 == cr && --rr != j) {
s.swap(rr, j);
}
}
if (i < j) s.swap(i, j);
else break;
}
j = i;
// swap pivot- and all eq values- into position
while (ll >= p) {
s.swap(ll--, --i);
}
while (rr < r) {
s.swap(rr++, j++);
}
// Conquer
// Recurse on smaller interval first to keep stack shallow
assert i != j;
if (i - p < r - j) {
sortInternal(s, p, i, rep, depth);
p = j;
} else {
sortInternal(s, j, r, rep, depth);
r = i;
}
}
}
}
