/*
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* Copyright 2006 The Android Open Source Project
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*
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* Use of this source code is governed by a BSD-style license that can be
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* found in the LICENSE file.
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*/
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#ifndef SkTSort_DEFINED
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#define SkTSort_DEFINED
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#include "SkMathPriv.h"
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#include "SkTo.h"
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#include "SkTypes.h"
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#include <utility>
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/* A comparison functor which performs the comparison 'a < b'. */
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template <typename T> struct SkTCompareLT {
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bool operator()(const T a, const T b) const { return a < b; }
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};
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/* A comparison functor which performs the comparison '*a < *b'. */
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template <typename T> struct SkTPointerCompareLT {
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bool operator()(const T* a, const T* b) const { return *a < *b; }
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};
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///////////////////////////////////////////////////////////////////////////////
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/* Sifts a broken heap. The input array is a heap from root to bottom
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* except that the root entry may be out of place.
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*
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* Sinks a hole from array[root] to leaf and then sifts the original array[root] element
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* from the leaf level up.
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*
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* This version does extra work, in that it copies child to parent on the way down,
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* then copies parent to child on the way back up. When copies are inexpensive,
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* this is an optimization as this sift variant should only be used when
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* the potentially out of place root entry value is expected to be small.
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*
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* @param root the one based index into array of the out-of-place root of the heap.
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* @param bottom the one based index in the array of the last entry in the heap.
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*/
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template <typename T, typename C>
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void SkTHeapSort_SiftUp(T array[], size_t root, size_t bottom, C lessThan) {
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T x = array[root-1];
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size_t start = root;
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size_t j = root << 1;
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while (j <= bottom) {
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if (j < bottom && lessThan(array[j-1], array[j])) {
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++j;
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}
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array[root-1] = array[j-1];
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root = j;
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j = root << 1;
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}
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j = root >> 1;
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while (j >= start) {
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if (lessThan(array[j-1], x)) {
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array[root-1] = array[j-1];
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root = j;
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j = root >> 1;
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} else {
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break;
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}
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}
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array[root-1] = x;
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}
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/* Sifts a broken heap. The input array is a heap from root to bottom
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* except that the root entry may be out of place.
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*
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* Sifts the array[root] element from the root down.
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*
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* @param root the one based index into array of the out-of-place root of the heap.
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* @param bottom the one based index in the array of the last entry in the heap.
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*/
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template <typename T, typename C>
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void SkTHeapSort_SiftDown(T array[], size_t root, size_t bottom, C lessThan) {
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T x = array[root-1];
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size_t child = root << 1;
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while (child <= bottom) {
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if (child < bottom && lessThan(array[child-1], array[child])) {
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++child;
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}
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if (lessThan(x, array[child-1])) {
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array[root-1] = array[child-1];
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root = child;
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child = root << 1;
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} else {
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break;
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}
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}
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array[root-1] = x;
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}
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/** Sorts the array of size count using comparator lessThan using a Heap Sort algorithm. Be sure to
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* specialize swap if T has an efficient swap operation.
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*
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* @param array the array to be sorted.
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* @param count the number of elements in the array.
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* @param lessThan a functor with bool operator()(T a, T b) which returns true if a comes before b.
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*/
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template <typename T, typename C> void SkTHeapSort(T array[], size_t count, C lessThan) {
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for (size_t i = count >> 1; i > 0; --i) {
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SkTHeapSort_SiftDown(array, i, count, lessThan);
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}
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for (size_t i = count - 1; i > 0; --i) {
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using std::swap;
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swap(array[0], array[i]);
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SkTHeapSort_SiftUp(array, 1, i, lessThan);
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}
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}
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/** Sorts the array of size count using comparator '<' using a Heap Sort algorithm. */
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template <typename T> void SkTHeapSort(T array[], size_t count) {
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SkTHeapSort(array, count, SkTCompareLT<T>());
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}
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///////////////////////////////////////////////////////////////////////////////
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/** Sorts the array of size count using comparator lessThan using an Insertion Sort algorithm. */
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template <typename T, typename C> static void SkTInsertionSort(T* left, T* right, C lessThan) {
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for (T* next = left + 1; next <= right; ++next) {
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if (!lessThan(*next, *(next - 1))) {
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continue;
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}
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T insert = std::move(*next);
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T* hole = next;
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do {
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*hole = std::move(*(hole - 1));
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--hole;
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} while (left < hole && lessThan(insert, *(hole - 1)));
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*hole = std::move(insert);
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}
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}
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///////////////////////////////////////////////////////////////////////////////
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template <typename T, typename C>
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static T* SkTQSort_Partition(T* left, T* right, T* pivot, C lessThan) {
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using std::swap;
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T pivotValue = *pivot;
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swap(*pivot, *right);
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T* newPivot = left;
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while (left < right) {
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if (lessThan(*left, pivotValue)) {
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swap(*left, *newPivot);
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newPivot += 1;
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}
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left += 1;
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}
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swap(*newPivot, *right);
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return newPivot;
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}
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/* Intro Sort is a modified Quick Sort.
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* When the region to be sorted is a small constant size it uses Insertion Sort.
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* When depth becomes zero, it switches over to Heap Sort.
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* This implementation recurses on the left region after pivoting and loops on the right,
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* we already limit the stack depth by switching to heap sort,
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* and cache locality on the data appears more important than saving a few stack frames.
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*
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* @param depth at this recursion depth, switch to Heap Sort.
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* @param left the beginning of the region to be sorted.
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* @param right the end of the region to be sorted (inclusive).
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* @param lessThan a functor with bool operator()(T a, T b) which returns true if a comes before b.
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*/
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template <typename T, typename C> void SkTIntroSort(int depth, T* left, T* right, C lessThan) {
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while (true) {
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if (right - left < 32) {
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SkTInsertionSort(left, right, lessThan);
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return;
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}
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if (depth == 0) {
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SkTHeapSort<T>(left, right - left + 1, lessThan);
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return;
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}
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--depth;
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T* pivot = left + ((right - left) >> 1);
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pivot = SkTQSort_Partition(left, right, pivot, lessThan);
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SkTIntroSort(depth, left, pivot - 1, lessThan);
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left = pivot + 1;
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}
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}
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/** Sorts the region from left to right using comparator lessThan using a Quick Sort algorithm. Be
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* sure to specialize swap if T has an efficient swap operation.
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*
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* @param left the beginning of the region to be sorted.
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* @param right the end of the region to be sorted (inclusive).
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* @param lessThan a functor with bool operator()(T a, T b) which returns true if a comes before b.
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*/
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template <typename T, typename C> void SkTQSort(T* left, T* right, C lessThan) {
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if (left >= right) {
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return;
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}
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// Limit Intro Sort recursion depth to no more than 2 * ceil(log2(n)).
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int depth = 2 * SkNextLog2(SkToU32(right - left));
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SkTIntroSort(depth, left, right, lessThan);
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}
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/** Sorts the region from left to right using comparator '<' using a Quick Sort algorithm. */
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template <typename T> void SkTQSort(T* left, T* right) {
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SkTQSort(left, right, SkTCompareLT<T>());
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}
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/** Sorts the region from left to right using comparator '* < *' using a Quick Sort algorithm. */
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template <typename T> void SkTQSort(T** left, T** right) {
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SkTQSort(left, right, SkTPointerCompareLT<T>());
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}
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#endif
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