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/****************************************************************************
 *   Copyright (C) 2011 by Claas Anders "CaScAdE" Rathje                    *
 *   admiralcascade@gmail.com                                               *
 *   Project-URL: http://www.mylifesucks.de/oss/c-epilepsy/                 *
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 ****************************************************************************/

#include "integer_math.h"

/*
   CORDIC atan2 generated by http://vivara.net/cgi-bin/cordic.cgi?range=3600&n=10&size=int16_t

   send bugs to Mark Rages <markrages@gmail.com>

   result is one revolution per 3600 counts.

   Performance test (error as percent of revolution):
        Maximum: +0.088%
           Mean:  0.006%
        Minimum: -0.085%
      mean(abs):  0.029%  
            rms:  0.001%
 */

int16_t atan2_fp(int16_t y, int16_t x) {

    const int16_t cordic[] = {450, 266, 140, 71, 36, 18, 9, 4, 2, 1};
    int16_t theta;
    int16_t i;

    if (x < 0) {
        theta = 1800;
        x = -x;
        y = -y;
    } else {
        theta = 0;
    }

    for (i = 0; i < 10; i++) {
        int16_t last_x;

        last_x = x;

        if (y < 0) { // sign=1
            x -= y >> i;
            y += last_x >> i;
            theta -= cordic[i];
        } else {
            x += y >> i;
            y -= last_x >> i;
            theta += cordic[i];
        }
    }

#ifdef CORDIC_DEBUG  
    printf("%d", theta);
    printf(" %lld\n", ((long long int)x) * 155L / 256);
#endif

    return theta % 3600;
}