gnulib/lib/sqrtl.c

/* Emulation for sqrtl.
   Contributed by Paolo Bonzini

   Copyright 2002-2003, 2007, 2009-2020 Free Software Foundation, Inc.

   This file is part of gnulib.

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */

#include <config.h>

/* Specification.  */
#include <math.h>

#if HAVE_SAME_LONG_DOUBLE_AS_DOUBLE

long double
sqrtl (long double x)
{
  return sqrt (x);
}

#else

# include <float.h>

/* A simple Newton-Raphson method. */
long double
sqrtl (long double x)
{
  long double delta, y;
  int exponent;

  /* Check for NaN */
  if (isnanl (x))
    return x;

  /* Check for negative numbers */
  if (x < 0.0L)
    return (long double) sqrt (-1);

  /* Check for zero and infinites */
  if (x + x == x)
    return x;

  frexpl (x, &exponent);
  y = ldexpl (x, -exponent / 2);

  do
    {
      delta = y;
      y = (y + x / y) * 0.5L;
      delta -= y;
    }
  while (delta != 0.0L);

  return y;
}

#endif