/*
* RapidMiner
*
* Copyright (C) 2001-2011 by Rapid-I and the contributors
*
* Complete list of developers available at our web site:
*
* http://rapid-i.com
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* 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 Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see http://www.gnu.org/licenses/.
*/
package liblinear;
final class ArraySorter {
/**
* <p>Sorts the specified array of doubles into <b>descending</b> order.</p>
*
* <em>This code is borrowed from Sun's JDK 1.6.0.07</em>
*/
public static void reversedMergesort( double[] a ) {
reversedMergesort(a, 0, a.length);
}
private static void reversedMergesort( double x[], int off, int len ) {
// Insertion sort on smallest arrays
if ( len < 7 ) {
for ( int i = off; i < len + off; i++ )
for ( int j = i; j > off && x[j - 1] < x[j]; j-- )
swap(x, j, j - 1);
return;
}
// Choose a partition element, v
int m = off + (len >> 1); // Small arrays, middle element
if ( len > 7 ) {
int l = off;
int n = off + len - 1;
if ( len > 40 ) { // Big arrays, pseudomedian of 9
int s = len / 8;
l = med3(x, l, l + s, l + 2 * s);
m = med3(x, m - s, m, m + s);
n = med3(x, n - 2 * s, n - s, n);
}
m = med3(x, l, m, n); // Mid-size, med of 3
}
double v = x[m];
// Establish Invariant: v* (<v)* (>v)* v*
int a = off, b = a, c = off + len - 1, d = c;
while ( true ) {
while ( b <= c && x[b] >= v ) {
if ( x[b] == v ) swap(x, a++, b);
b++;
}
while ( c >= b && x[c] <= v ) {
if ( x[c] == v ) swap(x, c, d--);
c--;
}
if ( b > c ) break;
swap(x, b++, c--);
}
// Swap partition elements back to middle
int s, n = off + len;
s = Math.min(a - off, b - a);
vecswap(x, off, b - s, s);
s = Math.min(d - c, n - d - 1);
vecswap(x, b, n - s, s);
// Recursively sort non-partition-elements
if ( (s = b - a) > 1 ) reversedMergesort(x, off, s);
if ( (s = d - c) > 1 ) reversedMergesort(x, n - s, s);
}
/**
* Swaps x[a] with x[b].
*/
private static void swap( double x[], int a, int b ) {
double t = x[a];
x[a] = x[b];
x[b] = t;
}
/**
* Swaps x[a .. (a+n-1)] with x[b .. (b+n-1)].
*/
private static void vecswap( double x[], int a, int b, int n ) {
for ( int i = 0; i < n; i++, a++, b++ )
swap(x, a, b);
}
/**
* Returns the index of the median of the three indexed doubles.
*/
private static int med3( double x[], int a, int b, int c ) {
return (x[a] < x[b] ? (x[b] < x[c] ? b : x[a] < x[c] ? c : a) : (x[b] > x[c] ? b : x[a] > x[c] ? c : a));
}
}