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diff --git a/gr-digital/include/digital_additive_scrambler_bb.h b/gr-digital/include/digital_additive_scrambler_bb.h
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+/* -*- c++ -*- */
+/*
+ * Copyright 2008,2010,2012 Free Software Foundation, Inc.
+ *
+ * This file is part of GNU Radio
+ *
+ * GNU Radio is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3, or (at your option)
+ * any later version.
+ *
+ * GNU Radio 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with GNU Radio; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+#ifndef INCLUDED_GR_ADDITIVE_SCRAMBLER_BB_H
+#define INCLUDED_GR_ADDITIVE_SCRAMBLER_BB_H
+
+#include <digital_api.h>
+#include <gr_sync_block.h>
+#include <gri_lfsr.h>
+
+class digital_additive_scrambler_bb;
+typedef boost::shared_ptr<digital_additive_scrambler_bb> digital_additive_scrambler_bb_sptr;
+
+DIGITAL_API digital_additive_scrambler_bb_sptr
+digital_make_additive_scrambler_bb(int mask, int seed,
+				   int len, int count=0);
+
+/*!
+ * Scramble an input stream using an LFSR.  This block works on the LSB only
+ * of the input data stream, i.e., on an "unpacked binary" stream, and
+ * produces the same format on its output.
+ *
+ * \param mask     Polynomial mask for LFSR
+ * \param seed     Initial shift register contents
+ * \param len      Shift register length
+ * \param count    Number of bits after which shift register is reset, 0=never
+ *
+ * The scrambler works by XORing the incoming bit stream by the output of
+ * the LFSR.  Optionally, after 'count' bits have been processed, the shift
+ * register is reset to the seed value.  This allows processing fixed length
+ * vectors of samples.
+ *
+ * \ingroup coding_blk
+ */
+
+class DIGITAL_API digital_additive_scrambler_bb : public gr_sync_block
+{
+  friend DIGITAL_API digital_additive_scrambler_bb_sptr
+    digital_make_additive_scrambler_bb(int mask, int seed,
+				       int len, int count);
+
+  gri_lfsr d_lfsr;
+  int      d_count;
+  int      d_bits;
+
+  digital_additive_scrambler_bb(int mask, int seed,
+				int len, int count);
+
+public:
+  int work(int noutput_items,
+	   gr_vector_const_void_star &input_items,
+	   gr_vector_void_star &output_items);
+};
+
+#endif /* INCLUDED_GR_ADDITIVE_SCRAMBLER_BB_H */