nuttx/libs/libc/math/lib_atanh.c

/****************************************************************************
 * libs/libc/math/lib_atanh.c
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ****************************************************************************/

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

#include <nuttx/config.h>
#include <nuttx/compiler.h>

#include <math.h>

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

#ifdef CONFIG_HAVE_DOUBLE
double atanh(double x)
{
  double y;

  if (fabs(x) < 1E-5)
    {
      double z = x * x;

      /* x + 1/3 * x^3 + 1/5 * x^5 + 1/7 * x^7 + ... */

      y = x * (1 + z / 3.0);
    }
  else
    {
      y = log((1 + x) / (1 - x)) / 2.0;
    }

  return y;
}
#endif