fxpt.h

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/* -*- c++ -*- */
/*
 * Copyright 2004,2013 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_FXPT_H
#define INCLUDED_GR_FXPT_H

#include <gnuradio/api.h>
#include <gnuradio/types.h>
#include <stdint.h>

namespace gr {

  /*!
   * \brief fixed point sine and cosine and friends.
   * \ingroup misc
   *
   *   fixed pt radians
   *  --------- --------
   *   -2**31       -pi
   *        0         0
   *  2**31-1        pi - epsilon
   */
  class GR_RUNTIME_API fxpt
  {
    static const int WORDBITS = 32;
    static const int NBITS = 10;
    static const float s_sine_table[1 << NBITS][2];
    static const float PI;
    static const float TAU;
    static const float TWO_TO_THE_31;

  public:
    static int32_t
      float_to_fixed(float x)
    {
      // Fold x into -PI to PI.
      int d = (int)std::floor(x/TAU+0.5);
      x -= d*TAU;
      // And convert to an integer.
      return (int32_t) ((float) x * TWO_TO_THE_31 / PI);
    }

    static float
      fixed_to_float (int32_t x)
    {
      return x * (PI / TWO_TO_THE_31);
    }

    /*!
     * \brief Given a fixed point angle x, return float sine (x)
     */
    static float
      sin(int32_t x)
    {
      uint32_t ux = x;
      int index = ux >> (WORDBITS - NBITS);
      return s_sine_table[index][0] * (ux >> 1) + s_sine_table[index][1];
    }

    /*
     * \brief Given a fixed point angle x, return float cosine (x)
     */
    static float
      cos (int32_t x)
    {
      uint32_t ux = x + 0x40000000;
      int index = ux >> (WORDBITS - NBITS);
      return s_sine_table[index][0] * (ux >> 1) + s_sine_table[index][1];
    }

    /*
     * \brief Given a fixedpoint angle x, return float cos(x) and sin (x)
     */
    static void sincos(int32_t x, float *s, float *c)
    {
      uint32_t ux = x;
      int sin_index = ux >> (WORDBITS - NBITS);
      *s = s_sine_table[sin_index][0] * (ux >> 1) + s_sine_table[sin_index][1];

      ux = x + 0x40000000;
      int cos_index = ux >> (WORDBITS - NBITS);
      *c = s_sine_table[cos_index][0] * (ux >> 1) + s_sine_table[cos_index][1];

      return;
    }

  };

} /* namespace gr */

#endif /* INCLUDED_GR_FXPT_H */