lib/hypotl.c

   1 /* Hypotenuse of a right-angled triangle.
   2    Copyright (C) 2012-2018 Free Software Foundation, Inc.
   3
   4    This program is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 3 of the License, or
   7    (at your option) any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 /* Written by Bruno Haible <bruno@clisp.org>, 2012.  */
  18
  19 #include <config.h>
  20
  21 /* Specification.  */
  22 #include <math.h>
  23
  24 #if HAVE_SAME_LONG_DOUBLE_AS_DOUBLE
  25
  26 long double
  27 hypotl (long double x, long double y)
  28 {
  29   return hypot (x, y);
  30 }
  31
  32 #else
  33
  34 long double
  35 hypotl (long double x, long double y)
  36 {
  37   if (isfinite (x) && isfinite (y))
  38     {
  39       /* Determine absolute values.  */
  40       x = fabsl (x);
  41       y = fabsl (y);
  42
  43       {
  44         /* Find the bigger and the smaller one.  */
  45         long double a;
  46         long double b;
  47
  48         if (x >= y)
  49           {
  50             a = x;
  51             b = y;
  52           }
  53         else
  54           {
  55             a = y;
  56             b = x;
  57           }
  58         /* Now 0 <= b <= a.  */
  59
  60         {
  61           int e;
  62           long double an;
  63           long double bn;
  64
  65           /* Write a = an * 2^e, b = bn * 2^e with 0 <= bn <= an < 1.  */
  66           an = frexpl (a, &e);
  67           bn = ldexpl (b, - e);
  68
  69           {
  70             long double cn;
  71
  72             /* Through the normalization, no unneeded overflow or underflow
  73                will occur here.  */
  74             cn = sqrtl (an * an + bn * bn);
  75             return ldexpl (cn, e);
  76           }
  77         }
  78       }
  79     }
  80   else
  81     {
  82       if (isinf (x) || isinf (y))
  83         /* x or y is infinite.  Return +Infinity.  */
  84         return HUGE_VALL;
  85       else
  86         /* x or y is NaN.  Return NaN.  */
  87         return x + y;
  88     }
  89 }
  90
  91 #endif