statistical encoding

brouter-codec/src/main/java/btools/codec/IntegerFifo3Pass.java

@@ -0,0 +1,62 @@
+package btools.codec;
+
+/**
+ * Special integer fifo suitable for 3-pass encoding
+ */
+public class IntegerFifo3Pass
+{
+  private int[] a;
+  private int size;
+  private int pos;
+
+  private int pass;
+
+  public IntegerFifo3Pass( int capacity )
+  {
+    a = capacity < 4 ? new int[4] : new int[capacity];
+  }
+
+  /**
+   * Starts a new encoding pass and resets the reading pointer
+   * from the stats collected in pass2 and writes that to the given context
+   */
+  public void init()
+  {
+    pass++;
+    pos = 0;
+  }
+
+  /**
+   * writes to the fifo in pass2
+   */
+  public void add( int value )
+  {
+    if ( pass == 2 )
+    {
+      if ( size == a.length )
+      {
+        int[] aa = new int[2 * size];
+        System.arraycopy( a, 0, aa, 0, size );
+        a = aa;
+      }
+      a[size++] = value;
+    }
+  }
+
+  /**
+   * reads from the fifo in pass3 (in pass1/2 returns just 1)
+   */
+  public int getNext()
+  {
+    return pass == 3 ? get( pos++ ) : 1;
+  }
+
+  private int get( int idx )
+  {
+    if ( idx >= size )
+    {
+      throw new IndexOutOfBoundsException( "list size=" + size + " idx=" + idx );
+    }
+    return a[idx];
+  }
+}