sliding_correlator_impl.h

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/* -*- c++ -*- */
/*
 * Copyright 2002 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_SLIDING_CORRELATOR_H_
#define _ATSC_SLIDING_CORRELATOR_H_

#include <gnuradio/atsc/api.h>
#include <string.h>

#include <gnuradio/atsc/pnXXX_impl.h>
// extern const unsigned char atsc_pn511[511];
// extern const unsigned char atsc_pn63[63];

/*!
 * \brief look for the PN 511 field sync pattern
 */
class ATSC_API atsci_sliding_correlator
{
public:
    atsci_sliding_correlator();
    ~atsci_sliding_correlator(){};

    //! input hard decision bit, return correlation (0,511)
    // Result is the number of wrong bits.
    // E.g., 0 -> perfect match; 511 -> all bits are wrong

    int input_bit(int bit);

    //! input sample, return correlation (0,511)
    // Result is the number of wrong bits.
    // E.g., 0 -> perfect match; 511 -> all bits are wrong

    int input_int(int sample) { return input_bit(sample < 0 ? 0 : 1); }

    //! input sample, return correlation (0,511)
    // Result is the number of wrong bits.
    // E.g., 0 -> perfect match; 511 -> all bits are wrong

    int input_float(float sample) { return input_bit(sample < 0 ? 0 : 1); }

    void reset() { input.reset(); }

private:
    typedef unsigned long srblock;
    static const int bits_per_char = 8;
    static const int srblock_bitsize = sizeof(srblock) * bits_per_char;
    static const int NSRBLOCKS = (511 + srblock_bitsize - 1) / srblock_bitsize;

    class shift_reg
    {
    public:
        shift_reg() { reset(); }
        void reset() { memset(d, 0, sizeof(d)); }
        void shift_in(int bit);
        srblock d[NSRBLOCKS];
    };

    shift_reg mask;     // pattern we're looking for
    shift_reg input;    // current input window
    shift_reg and_mask; // bits to consider
};

#endif /* _ATSC_SLIDING_CORRELATOR_H_ */