/*

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code 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

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package sun.java2d.marlin;

/**

 * MergeSort adapted from (OpenJDK 8) java.util.Array.legacyMergeSort(Object[])

 * to swap two arrays at the same time (x & y)

 * and use external auxiliary storage for temporary arrays

 */

final class MergeSort {

    // insertion sort threshold

    public static final int INSERTION_SORT_THRESHOLD = 14;

    /**

     * Modified merge sort:

     * Input arrays are in both auxX/auxY (sorted: 0 to insertionSortIndex)

     *                     and x/y (unsorted: insertionSortIndex to toIndex)

     * Outputs are stored in x/y arrays

     */

    static void mergeSortNoCopy(final int[] x, final int[] y,

                                final int[] auxX, final int[] auxY,

                                final int toIndex,

                                final int insertionSortIndex)

    {

        if ((toIndex > x.length) || (toIndex > y.length)

                || (toIndex > auxX.length) || (toIndex > auxY.length)) {

            // explicit check to avoid bound checks within hot loops (below):

            throw new ArrayIndexOutOfBoundsException("bad arguments: toIndex="

                                                     + toIndex);

        }

        // sort second part only using merge / insertion sort

        // in auxiliary storage (auxX/auxY)

        mergeSort(x, y, x, auxX, y, auxY, insertionSortIndex, toIndex);

        // final pass to merge both

        // Merge sorted parts (auxX/auxY) into x/y arrays

        if ((insertionSortIndex == 0)

            || (auxX[insertionSortIndex - 1] <= auxX[insertionSortIndex])) {

            // 34 occurences

            // no initial left part or both sublists (auxX, auxY) are sorted:

            // copy back data into (x, y):

            System.arraycopy(auxX, 0, x, 0, toIndex);

            System.arraycopy(auxY, 0, y, 0, toIndex);

            return;

        }

        for (int i = 0, p = 0, q = insertionSortIndex; i < toIndex; i++) {

            if ((q >= toIndex) || ((p < insertionSortIndex)

                                   && (auxX[p] <= auxX[q]))) {

                x[i] = auxX[p];

                y[i] = auxY[p];

                p++;

            } else {

                x[i] = auxX[q];

                y[i] = auxY[q];

                q++;

            }

        }

    }

    /**

     * Src is the source array that starts at index 0

     * Dest is the (possibly larger) array destination with a possible offset

     * low is the index in dest to start sorting

     * high is the end index in dest to end sorting

     */

    private static void mergeSort(final int[] refX, final int[] refY,

                                  final int[] srcX, final int[] dstX,

                                  final int[] srcY, final int[] dstY,

                                  final int low, final int high)

    {

        final int length = high - low;

        /*

         * Tuning parameter: list size at or below which insertion sort

         * will be used in preference to mergesort.

         */

        if (length <= INSERTION_SORT_THRESHOLD) {

            // Insertion sort on smallest arrays

            dstX[low] = refX[low];

            dstY[low] = refY[low];

            for (int i = low + 1, j = low, x, y; i < high; j = i++) {

                x = refX[i];

                y = refY[i];

                while (dstX[j] > x) {

                    // swap element

                    dstX[j + 1] = dstX[j];

                    dstY[j + 1] = dstY[j];

                    if (j-- == low) {

                        break;

                    }

                }

                dstX[j + 1] = x;

                dstY[j + 1] = y;

            }

            return;

        }

        // Recursively sort halves of dest into src

        // note: use signed shift (not >>>) for performance

        // as indices are small enough to exceed Integer.MAX_VALUE

        final int mid = (low + high) >> 1;

        mergeSort(refX, refY, dstX, srcX, dstY, srcY, low, mid);

        mergeSort(refX, refY, dstX, srcX, dstY, srcY, mid, high);

        // If arrays are inverted ie all(A) > all(B) do swap A and B to dst

        if (srcX[high - 1] <= srcX[low]) {

            // 1561 occurences

            final int left = mid - low;

            final int right = high - mid;

            final int off = (left != right) ? 1 : 0;

            // swap parts:

            System.arraycopy(srcX, low, dstX, mid + off, left);

            System.arraycopy(srcX, mid, dstX, low, right);

            System.arraycopy(srcY, low, dstY, mid + off, left);

            System.arraycopy(srcY, mid, dstY, low, right);

            return;

        }

        // If arrays are already sorted, just copy from src to dest.  This is an

        // optimization that results in faster sorts for nearly ordered lists.

        if (srcX[mid - 1] <= srcX[mid]) {

            // 14 occurences

            System.arraycopy(srcX, low, dstX, low, length);

            System.arraycopy(srcY, low, dstY, low, length);

            return;

        }

        // Merge sorted halves (now in src) into dest

        for (int i = low, p = low, q = mid; i < high; i++) {

            if ((q >= high) || ((p < mid) && (srcX[p] <= srcX[q]))) {

                dstX[i] = srcX[p];

                dstY[i] = srcY[p];

                p++;

            } else {

                dstX[i] = srcX[q];

                dstY[i] = srcY[q];

                q++;

            }

        }

    }

    private MergeSort() {

    }

}