/**
 * This file has no copyright assigned and is placed in the Public Domain.
 * This file is part of the mingw-w64 runtime package.
 * No warranty is given; refer to the file DISCLAIMER.PD within this package.
 */

#include <math.h>

double acosh(double x)
{
  if (x < 1.0)
    return NAN;
  if (isinf(x*x))
    return log(2) + log(x);
  return log(x + sqrt(x*x - 1));
}