--- /dev/null
+/* -*- 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_EQUALIZER_H_
+#define _ATSC_EQUALIZER_H_
+
+#include <atsci_syminfo.h>
+
+/*!
+ * \brief abstract base class for ATSC equalizer
+ */
+class atsci_equalizer {
+
+private:
+
+ /*
+ * have we seen a field sync since the last reset or problem?
+ */
+ bool d_locked_p;
+
+ /*
+ * sample offset from the beginning of the last field sync we saw
+ * to the beginning of our current input stream. When we're locked
+ * this will be in [0, 313*832] i.e., [0, 260416]
+ */
+ int d_offset_from_last_field_sync;
+
+ int d_current_field; // [0,1]
+
+
+public:
+
+ // CREATORS
+ atsci_equalizer ();
+ virtual ~atsci_equalizer ();
+
+ // MANIPULATORS
+
+ /*!
+ * \brief reset state (e.g., on channel change)
+ *
+ * Note, subclasses must invoke the superclass's method too!
+ */
+ virtual void reset ();
+
+ /*!
+ * \brief produce \p nsamples of output from given inputs and tags
+ *
+ * This is the main entry point. It examines the input_tags
+ * and local state and invokes the appropriate virtual function
+ * to handle each sub-segment of the input data.
+ *
+ * \p input_samples must have (nsamples + ntaps() - 1) valid entries.
+ * input_samples[0] .. input_samples[nsamples - 1 + ntaps() - 1] are
+ * referenced to compute the output values.
+ *
+ * \p input_tags must have nsamples valid entries.
+ * input_tags[0] .. input_tags[nsamples - 1] are referenced to
+ * compute the output values.
+ */
+ virtual void filter (const float *input_samples,
+ const atsc::syminfo *input_tags,
+ float *output_samples,
+ int nsamples);
+
+ // ACCESSORS
+
+ /*!
+ * \brief how much history the input data stream requires.
+ *
+ * This must return a value >= 1. Think of this as the number
+ * of samples you need to look at to compute a single output sample.
+ */
+ virtual int ntaps () const = 0;
+
+ /*!
+ * \brief how many taps are "in the future".
+ *
+ * This allows us to handle what the ATSC folks call "pre-ghosts".
+ * What it really does is allow the caller to jack with the offset
+ * between the tags and the data so that everything magically works out.
+ *
+ * npretaps () must return a value between 0 and ntaps() - 1.
+ *
+ * If npretaps () returns 0, this means that the equalizer will only handle
+ * multipath "in the past." I suspect that a good value would be something
+ * like 15% - 20% of ntaps ().
+ */
+ virtual int npretaps () const = 0;
+
+
+protected:
+
+ /*!
+ * Input range is known NOT TO CONTAIN data segment syncs
+ * or field syncs. This should be the fast path. In the
+ * non decicion directed case, this just runs the input
+ * through the filter without adapting it.
+ *
+ * \p input_samples has (nsamples + ntaps() - 1) valid entries.
+ * input_samples[0] .. input_samples[nsamples - 1 + ntaps() - 1] may be
+ * referenced to compute the output values.
+ */
+ virtual void filter_normal (const float *input_samples,
+ float *output_samples,
+ int nsamples) = 0;
+
+ /*!
+ * Input range is known to consist of only a data segment sync or a
+ * portion of a data segment sync. \p nsamples will be in [1,4].
+ * \p offset will be in [0,3]. \p offset is the offset of the input
+ * from the beginning of the data segment sync pattern.
+ *
+ * \p input_samples has (nsamples + ntaps() - 1) valid entries.
+ * input_samples[0] .. input_samples[nsamples - 1 + ntaps() - 1] may be
+ * referenced to compute the output values.
+ */
+ virtual void filter_data_seg_sync (const float *input_samples,
+ float *output_samples,
+ int nsamples,
+ int offset) = 0;
+
+ /*!
+ * Input range is known to consist of only a field sync segment or a
+ * portion of a field sync segment. \p nsamples will be in [1,832].
+ * \p offset will be in [0,831]. \p offset is the offset of the input
+ * from the beginning of the data segment sync pattern. We consider the
+ * 4 symbols of the immediately preceding data segment sync to be the
+ * first symbols of the field sync segment. \p which_field is in [0,1]
+ * and specifies which field (duh).
+ *
+ * \p input_samples has (nsamples + ntaps() - 1) valid entries.
+ * input_samples[0] .. input_samples[nsamples - 1 + ntaps() - 1] may be
+ * referenced to compute the output values.
+ */
+ virtual void filter_field_sync (const float *input_samples,
+ float *output_samples,
+ int nsamples,
+ int offset,
+ int which_field) = 0;
+};
+
+
+#endif /* _ATSC_EQUALIZER_H_ */
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