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Diffstat (limited to 'gr-atsc/include/atsc/randomizer_impl.h')
-rw-r--r-- | gr-atsc/include/atsc/randomizer_impl.h | 97 |
1 files changed, 97 insertions, 0 deletions
diff --git a/gr-atsc/include/atsc/randomizer_impl.h b/gr-atsc/include/atsc/randomizer_impl.h new file mode 100644 index 0000000000..4fdbebc06d --- /dev/null +++ b/gr-atsc/include/atsc/randomizer_impl.h @@ -0,0 +1,97 @@ +/* -*- 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/api.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 ATSC_API 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_ */ |