heapsort.h

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// Copyright (C) 2002-2012 Nikolaus Gebhardt
// This file is part of the "Irrlicht Engine".
// For conditions of distribution and use, see copyright notice in irrlicht.h

#ifndef __IRR_HEAPSORT_H_INCLUDED__
#define __IRR_HEAPSORT_H_INCLUDED__

#include "irrTypes.h"

namespace irr
{
namespace core
{

template<class T>
inline void heapsink(T*array, s32 element, s32 max)
{
    while ((element<<1) < max) // there is a left child
    {
        s32 j = (element<<1);

        if (j+1 < max && array[j] < array[j+1])
            j = j+1; // take right child

        if (array[element] < array[j])
        {
            T t = array[j]; // swap elements
            array[j] = array[element];
            array[element] = t;
            element = j;
        }
        else
            return;
    }
}


template<class T>
inline void heapsort(T* array_, s32 size)
{
    // for heapsink we pretent this is not c++, where
    // arrays start with index 0. So we decrease the array pointer,
    // the maximum always +2 and the element always +1

    T* virtualArray = array_ - 1;
    s32 virtualSize = size + 2;
    s32 i;

    // build heap

    for (i=((size-1)/2); i>=0; --i)
        heapsink(virtualArray, i+1, virtualSize-1);

    // sort array, leave out the last element (0)
    for (i=size-1; i>0; --i)
    {
        T t = array_[0];
        array_[0] = array_[i];
        array_[i] = t;
        heapsink(virtualArray, 1, i + 1);
    }
}

} // end namespace core
} // end namespace irr

#endif