X-Git-Url: https://git.gag.com/?a=blobdiff_plain;f=gr-atsc%2Fsrc%2Flib%2Fatsci_randomizer.h;fp=gr-atsc%2Fsrc%2Flib%2Fatsci_randomizer.h;h=36025d10b8b4f295b9d63d8f06aa7b1151c1ef9d;hb=35e43e8d8c271e6842191cac3fc3f2f88a861183;hp=0000000000000000000000000000000000000000;hpb=ea29b08aeb54227e6628f655ccfdb96fe4d8c378;p=debian%2Fgnuradio

diff --git a/gr-atsc/src/lib/atsci_randomizer.h b/gr-atsc/src/lib/atsci_randomizer.h
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+/* -*- c++ -*- */
+/*
+ * Copyright 2001 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 _ATSC_RANDOMIZER_H_
+#define _ATSC_RANDOMIZER_H_
+
+#include <atsc_types.h>
+
+/*! 
+ * \brief ATSC data "whitener"
+ *
+ * The data randomizer described in ATSC standard A/53B.  
+ * See figure D4 on page 54.
+ */
+
+class atsci_randomizer {
+  friend class qa_atsci_randomizer;
+  
+ public:
+  atsci_randomizer();
+
+  /*! \brief reset randomizer LFSR
+   *
+   * must be called during the Data Segment Sync interval prior to the
+   * first data segment.  I.e., the LFSR is reset prior to the first
+   * field of each VSB data frame.
+   */
+  void reset ();
+
+  //! randomize (whiten) mpeg packet and remove leading MPEG-2 sync byte
+  void randomize (atsc_mpeg_packet_no_sync &out, const atsc_mpeg_packet &in);
+
+  //! derandomize (de-whiten) mpeg packet and add leading MPEG-2 sync byte
+  void derandomize (atsc_mpeg_packet &out, const atsc_mpeg_packet_no_sync &in);
+
+  unsigned int state() const { return d_state; }
+
+ private:
+  static void initialize_output_map ();
+  static unsigned char slow_output_map (int st);
+
+  static unsigned char fast_output_map (int st){
+    return s_output_map[(st & 0xb23c) >> 2]; // Magic const with 8 bits set improves cache 
+                                             // utilization.  The bits correspond to the taps
+					     // used in output calculation.  Others may be 
+					     // safely ignored.
+  }
+    
+  //! return current output value
+  unsigned char output (){
+    return fast_output_map (d_state);
+  }
+
+  //! clock LFSR; advance to next state.
+  void clk (){
+    if (d_state & 0x1)
+      d_state = ((d_state ^ MASK) >> 1) | 0x8000;
+    else
+      d_state = d_state >> 1;
+  }
+
+  //! return current output value and advance to next state
+  unsigned char output_and_clk (){
+    unsigned char r = output ();
+    clk ();
+    return r;
+  }
+
+  unsigned int		    d_state;
+
+  static const unsigned int PRELOAD_VALUE = 0x018f; /* 0xf180 bit reversed */
+  static const unsigned int MASK = 0xa638;
+  static unsigned char 	    s_output_map[1 << 14];
+  static bool 		    s_output_map_initialized_p;
+};
+
+#endif /* _ATSC_RANDOMIZER_H_ */