cordic.c

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/*
 * Copyright (c) 2011 Broadcom Corporation
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */
#include <linux/module.h>
#include <linux/cordic.h>

#define CORDIC_ANGLE_GEN    39797
#define CORDIC_PRECISION_SHIFT  16
#define CORDIC_NUM_ITER     (CORDIC_PRECISION_SHIFT + 2)

#define FIXED(X)    ((s32)((X) << CORDIC_PRECISION_SHIFT))
#define FLOAT(X)    (((X) >= 0) \
        ? ((((X) >> (CORDIC_PRECISION_SHIFT - 1)) + 1) >> 1) \
        : -((((-(X)) >> (CORDIC_PRECISION_SHIFT - 1)) + 1) >> 1))

static const s32 arctan_table[] = {
    2949120,
    1740967,
    919879,
    466945,
    234379,
    117304,
    58666,
    29335,
    14668,
    7334,
    3667,
    1833,
    917,
    458,
    229,
    115,
    57,
    29
};

/*
 * cordic_calc_iq() - calculates the i/q coordinate for given angle
 *
 * theta: angle in degrees for which i/q coordinate is to be calculated
 * coord: function output parameter holding the i/q coordinate
 */
struct cordic_iq cordic_calc_iq(s32 theta)
{
    struct cordic_iq coord;
    s32 angle, valtmp;
    unsigned iter;
    int signx = 1;
    int signtheta;

    coord.i = CORDIC_ANGLE_GEN;
    coord.q = 0;
    angle = 0;

    theta = FIXED(theta);
    signtheta = (theta < 0) ? -1 : 1;
    theta = ((theta + FIXED(180) * signtheta) % FIXED(360)) -
        FIXED(180) * signtheta;

    if (FLOAT(theta) > 90) {
        theta -= FIXED(180);
        signx = -1;
    } else if (FLOAT(theta) < -90) {
        theta += FIXED(180);
        signx = -1;
    }

    for (iter = 0; iter < CORDIC_NUM_ITER; iter++) {
        if (theta > angle) {
            valtmp = coord.i - (coord.q >> iter);
            coord.q += (coord.i >> iter);
            angle += arctan_table[iter];
        } else {
            valtmp = coord.i + (coord.q >> iter);
            coord.q -= (coord.i >> iter);
            angle -= arctan_table[iter];
        }
        coord.i = valtmp;
    }

    coord.i *= signx;
    coord.q *= signx;
    return coord;
}
EXPORT_SYMBOL(cordic_calc_iq);

MODULE_DESCRIPTION("CORDIC algorithm");
MODULE_AUTHOR("Broadcom Corporation");
MODULE_LICENSE("Dual BSD/GPL");