lib/sqrtl.c

   1 /* Emulation for sqrtl.
   2    Contributed by Paolo Bonzini
   3
   4    Copyright 2002-2003, 2007, 2009-2019 Free Software Foundation, Inc.
   5
   6    This file is part of gnulib.
   7
   8    This program is free software: you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 3 of the License, or
  11    (at your option) any later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  20
  21 #include <config.h>
  22
  23 /* Specification.  */
  24 #include <math.h>
  25
  26 #if HAVE_SAME_LONG_DOUBLE_AS_DOUBLE
  27
  28 long double
  29 sqrtl (long double x)
  30 {
  31   return sqrt (x);
  32 }
  33
  34 #else
  35
  36 # include <float.h>
  37
  38 /* A simple Newton-Raphson method. */
  39 long double
  40 sqrtl (long double x)
  41 {
  42   long double delta, y;
  43   int exponent;
  44
  45   /* Check for NaN */
  46   if (isnanl (x))
  47     return x;
  48
  49   /* Check for negative numbers */
  50   if (x < 0.0L)
  51     return (long double) sqrt (-1);
  52
  53   /* Check for zero and infinites */
  54   if (x + x == x)
  55     return x;
  56
  57   frexpl (x, &exponent);
  58   y = ldexpl (x, -exponent / 2);
  59
  60   do
  61     {
  62       delta = y;
  63       y = (y + x / y) * 0.5L;
  64       delta -= y;
  65     }
  66   while (delta != 0.0L);
  67
  68   return y;
  69 }
  70
  71 #endif