[libc] [llvm] [libc][stdlib] Implement heap sort. (PR #98582)

[via llvm-commits]

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+//===-- Implementation of heap sort -----------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDLIB_HEAP_SORT_H
+#define LLVM_LIBC_SRC_STDLIB_HEAP_SORT_H
+
+#include "qsort_util.h"
+#include "src/__support/CPP/cstddef.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace internal {
+
+// A simple in-place heapsort implementation.
+// Follow the implementation in https://en.wikipedia.org/wiki/Heapsort.
+
+LIBC_INLINE void heap_sort(const Array &array) {
+  size_t end = array.size();
+  size_t start = end / 2;
+
+  auto left_child = [](size_t i) -> size_t { return 2 * i + 1; };
+
+  while (end > 1) {
+    if (start > 0) {
+      --start;
+    } else {
+      --end;
+      array.swap(0, end);
+    }
+
+    size_t root = start;
+    while (left_child(root) < end) {
+      size_t child = left_child(root);
+      if (child + 1 < end &&
+          array.elem_compare(child, array.get(child + 1)) < 0)
+        ++child;
+
+      if (array.elem_compare(root, array.get(child)) >= 0)
+        break;
+
+      array.swap(root, child);
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lntue wrote:

Done.

https://github.com/llvm/llvm-project/pull/98582