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 */