nuttx/libc/math/lib_sinh.c

/************************************************************************
 * libc/math/lib_sinh.c
 *
 * This file is a part of NuttX:
 *
 *   Copyright (C) 2012, 2015 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, 2010 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>

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

#ifdef CONFIG_HAVE_DOUBLE
double sinh(double x)
{
  double y;
  double z;

  if (fabs(x) < 1E-5)
    {
      /* x + 1/3! * x^3 + 1/5! * x^5 + 1/7! * x^7 + ... */

      z = x * x;
      y = x * (1.0 + z / 6.0);
    }
  else
    {
      z = exp(x);
      y = (z - 1.0 / z) / 2.0;
    }

  return y;
}
#endif