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