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/**
* Copyright © 2014 Mattias Andrée (maandree@member.fsf.org)
*
* 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 algorithms.shuffling;
import java.util.Random;
/**
* Bias free array shuffling class aiming to imitate card deck shuffling as preformed by humans
*/
public class CardShuffle
{
/**
* Calculates the floor of the binary logarithm of an integer
*
* @param x The integer
* @return The floored binary logarithm
*/
private static int lb(int x)
{
int rc = 0;
if ((x & 0xFFFF0000) != 0) { rc += 16; x >>= 16; }
if ((x & 0x0000FF00) != 0) { rc += 8; x >>= 8; }
if ((x & 0x000000F0) != 0) { rc += 4; x >>= 4; }
if ((x & 0x0000000C) != 0) { rc += 2; x >>= 2; }
if ((x & 0x00000002) != 0) rc += 1;
return rc;
}
£>for T in boolean char byte short int long float double Object; do
/**
* Shuffles an array
*
* @param array The array to shuffle
* @param random The random generator to use
*/
public static void shuffle(£{T}[] array, Random random)
{
int n;
int min = lb(n = array.length);
if (n < 2)
return;
£{T}[] left = new £{T}[n];
£{T}[] right = new £{T}[n];
int k = 0;
while ((k++ < min) || (random.nextInt(min) > 0))
{
int lcnt = 0;
int rcnt = 0;
for (int i = 0; i < n; i++)
if (random.nextInt(2) == 0)
left[lcnt++] = array[i];
else
right[rcnt++] = array[i];
int lptr = 0;
int rptr = 0;
for (int i = 0; i < n; i++)
array[i] = (lptr == lcnt) || ((rptr != rcnt) && (random.nextInt(2) == 0))
? right[rptr++] : left[lptr++];
}
}
£>done
}
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