text: /****************************************************************************
   * libc/math/lib_erfl.c
   *
   *   Copyright (C) 2015 Brennan Ashton. All rights reserved.
   *   Author: Brennan Ashton <bashton@brennanashton.com>
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in
   *    the documentation and/or other materials provided with the
   *    distribution.
   * 3. Neither the name NuttX nor the names of its contributors may be
   *    used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
   * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
   * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   * POSSIBILITY OF SUCH DAMAGE.
   *
   ****************************************************************************/
  
  /****************************************************************************
   * Included Files
   ****************************************************************************/
  
  #include <nuttx/config.h>
  #include <nuttx/compiler.h>
  
  #include <math.h>
  
  /****************************************************************************
   * Public Functions
   ****************************************************************************/
  
  #ifdef CONFIG_HAVE_LONG_DOUBLE
  long double erfl(long double x)
  {
    /* This implementation comes from the Handbook of Mathmatical Functions
     * The implementations in this book are not protected by copyright.
     * erf comes from formula 7.1.26
     */
  
    char sign;
    long double t;
    long double a1, a2, a3, a4, a5, p;
  
    a1 =  0.254829592;
    a2 = -0.284496736;
    a3 =  1.421413741;
    a4 = -1.453152027;
    a5 =  1.061405429;
    p  =  0.3275911;
  
    sign = (x >= 0 ? 1 : -1);
    t = 1.0/(1.0 + p*x);
    return sign * (1.0 - (((((a5 * t + a4) * t) + a3) * t + a2) * t + a1) * t * expf(-x * x));
  }
  #endif
  