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package com.sun.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
/**
* 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
/**
* 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
/**
* 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() {
}
}