px4-firmware/nuttx/libc/math/lib_asin.c

/************************************************************************
 * libc/math/lib_sin.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 <nuttx/config.h>
#include <nuttx/compiler.h>

#include <math.h>
#include <float.h>

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

#ifdef CONFIG_HAVE_DOUBLE
double asin(double x)
{
  long double y, y_sin, y_cos;

  y = 0;

  while (1)
    {
      y_sin = sin(y);
      y_cos = cos(y);

      if (y > M_PI_2 || y < -M_PI_2)
        {
          y = fmod(y, M_PI);
        }

      if (y_sin + DBL_EPSILON >= x && y_sin - DBL_EPSILON <= x)
        {
          break;
        }

      y = y - (y_sin - x) / y_cos;
    }

  return y;
}
#endif