1 files changed, 84 insertions, 0 deletions
diff --git a/src/algorithms/shuffling/CardShuffle.java b/src/algorithms/shuffling/CardShuffle.java
new file mode 100644
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--- /dev/null
+++ b/src/algorithms/shuffling/CardShuffle.java
@@ -0,0 +1,84 @@
+/**
+ * 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.arrays;
+
+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
+}
+