nuttx/libc/math/lib_atan2f.c

/************************************************************************
 * libc/math/lib_atan2f.c
 *
 * This file is a part of NuttX:
 *
 *   Copyright (C) 2012 Gregory Nutt. All rights reserved.
 *   Ported by: Darcy Gong
 *
 * It derives from the Rhombs OS math library by Nick Johnson which has
 * a compatibile, MIT-style license:
 *
 * Copyright (C) 2009-2011 Nick Johnson <nickbjohnson4224 at gmail.com>
 * 
 * Permission to use, copy, modify, and 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.
 *
 ************************************************************************/

/************************************************************************
 * Included Files
 ************************************************************************/

#include <math.h>

/************************************************************************
 * Public Functions
 ************************************************************************/

float atan2f(float y, float x)
{
  if (y == 0.0)
    {
      if (x >= 0.0)
        {
          return 0.0;
        }
      else
        {
          return M_PI;
        }
    }
  else if (y > 0.0)
    {
      if (x == 0.0)
        {
          return M_PI_2;
        }
      else if (x > 0.0)
        {
          return atanf(y / x);
        }
      else
        {
          return M_PI - atanf(y / x);
        }
    }
  else
    {
      if (x == 0.0)
        {
          return M_PI + M_PI_2;
        }
      else if (x > 0.0)
        {
          return 2 * M_PI - atanf(y / x);
        }
      else
        {
          return M_PI + atanf(y / x);
        }
    }
}