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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 */
|
