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+/** @file
+ * IPRT / No-CRT - Minimal C++ algorithm header.
+ */
+
+/*
+ * Copyright (C) 2022 Oracle and/or its affiliates.
+ *
+ * This file is part of VirtualBox base platform packages, as
+ * available from https://www.virtualbox.org.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, in version 3 of the
+ * License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses>.
+ *
+ * The contents of this file may alternatively be used under the terms
+ * of the Common Development and Distribution License Version 1.0
+ * (CDDL), a copy of it is provided in the "COPYING.CDDL" file included
+ * in the VirtualBox distribution, in which case the provisions of the
+ * CDDL are applicable instead of those of the GPL.
+ *
+ * You may elect to license modified versions of this file under the
+ * terms and conditions of either the GPL or the CDDL or both.
+ *
+ * SPDX-License-Identifier: GPL-3.0-only OR CDDL-1.0
+ */
+
+#ifndef VBOX_INCLUDED_SRC_nocrt_algorithm
+#define VBOX_INCLUDED_SRC_nocrt_algorithm
+#ifndef RT_WITHOUT_PRAGMA_ONCE
+# pragma once
+#endif
+
+#ifdef _MSC_VER
+# pragma warning(push)
+# pragma warning(disable: 4643) /* warning C4643: Forward declaring 'ios_base' in namespace std is not permitted by the C++ Standard */
+#endif
+
+namespace std
+{
+ /**
+ * Swap the values pointed to by the two references.
+ */
+ template<typename a_Type>
+ void swap(a_Type &a_rObj1, a_Type &a_rObj2)
+ {
+ a_Type Tmp(a_rObj1);
+ a_rObj1 = a_rObj2;
+ a_rObj2 = Tmp;
+ }
+
+ /**
+ * Swap the values pointed to by two forward iterators.
+ */
+ template<typename a_ForwardIt1, typename a_ForwardIt2>
+ void iter_swap(a_ForwardIt1 a_It1, a_ForwardIt2 a_It2)
+ {
+ swap(*a_It1, *a_It2);
+ }
+
+ template<typename a_RandomIt>
+ void sort(a_RandomIt a_ItBegin, a_RandomIt a_ItEnd)
+ {
+ /* Note! Using shell sort here because it's tiny and we've got code for it. */
+ /** @todo replace with faster code. */
+
+ /* Anything worth sorting? */
+ std::size_t const cElements = a_ItEnd - a_ItBegin;
+ if (cElements >= 1)
+ {
+ /* Loop on decreasing gap, ending with 1: */
+ std::size_t cGap = (cElements + 1) / 2;
+ while (cGap > 0)
+ {
+ /* Iterate from cGap till the end: */
+ for (std::size_t i = cGap; i < cElements; i++)
+ {
+ /* Find the best suitable location for the item at 'i' comparing
+ backwards in steps of 'cGap', swapping the item at 'i' with the
+ one at '-cGap*j' if it's smaller, stopping if it's larger.
+
+ Note! Original algorithm would make a copy of the item, this version
+ avoids extra copies of sorted items at the cost of extra copies
+ when dealing with unsorted ones a small cGaps values. */
+ a_RandomIt ItCur = a_ItBegin + i;
+ size_t j = i;
+ do
+ {
+ j -= cGap;
+ a_RandomIt ItAtGap = a_ItBegin + j;
+ if (*ItAtGap < *ItCur)
+ break;
+ std::iter_swap(ItAtGap, ItCur);
+ ItCur = ItAtGap;
+ } while (j >= cGap);
+ }
+
+ /* This does not generate the most optimal gap sequence, but it has the
+ advantage of being simple and avoid floating point. */
+ cGap /= 2;
+ }
+ }
+ }
+
+ template<typename a_RandomIt, typename a_FnCompareType>
+ void sort(a_RandomIt a_ItBegin, a_RandomIt a_ItEnd, a_FnCompareType a_fnComp)
+ {
+ /* Note! Using shell sort here because it's tiny and we've got code for it. */
+ /** @todo replace with faster code. */
+
+ /* Anything worth sorting? */
+ std::size_t const cElements = a_ItEnd - a_ItBegin;
+ if (cElements >= 1)
+ {
+ /* Loop on decreasing gap, ending with 1: */
+ std::size_t cGap = (cElements + 1) / 2;
+ while (cGap > 0)
+ {
+ /* Iterate from cGap till the end: */
+ for (std::size_t i = cGap; i < cElements; i++)
+ {
+ /* Find the best suitable location for the item at 'i' comparing
+ backwards in steps of 'cGap', swapping the item at 'i' with the
+ one at '-cGap*j' if it's smaller, stopping if it's larger.
+
+ Note! Original algorithm would make a copy of the item, this version
+ avoids extra copies of sorted items at the cost of extra copies
+ when dealing with unsorted ones a small cGaps values. */
+ a_RandomIt ItCur = a_ItBegin + i;
+ size_t j = i;
+ do
+ {
+ j -= cGap;
+ a_RandomIt ItAtGap = a_ItBegin + j;
+ if (a_fnComp(*ItAtGap, *ItCur))
+ break;
+ std::iter_swap(ItAtGap, ItCur);
+ ItCur = ItAtGap;
+ } while (j >= cGap);
+ }
+
+ /* This does not generate the most optimal gap sequence, but it has the
+ advantage of being simple and avoid floating point. */
+ cGap /= 2;
+ }
+ }
+ }
+
+}
+
+#ifdef _MSC_VER
+# pragma warning(pop)
+#endif
+
+#endif /* !VBOX_INCLUDED_SRC_nocrt_algorithm */
+