sysdeps/ieee754/ldbl-128ibm/s_roundevenl.c

   1 /* Round to nearest integer value, rounding halfway cases to even.
   2    ldbl-128ibm version.
   3    Copyright (C) 2016-2021 Free Software Foundation, Inc.
   4    This file is part of the GNU C Library.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <https://www.gnu.org/licenses/>.  */
  19
  20 #include <math.h>
  21 #include <math_private.h>
  22
  23 long double
  24 __roundevenl (long double x)
  25 {
  26   double xh, xl, hi;
  27
  28   ldbl_unpack (x, &xh, &xl);
  29
  30   if (xh != 0 && isfinite (xh))
  31     {
  32       hi = __roundeven (xh);
  33       if (hi != xh)
  34         {
  35           /* The high part is not an integer; the low part only
  36              affects the result if the high part is exactly half way
  37              between two integers and the low part is nonzero in the
  38              opposite direction to the rounding of the high part.  */
  39           double diff = hi - xh;
  40           if (fabs (diff) == 0.5)
  41             {
  42               if (xl < 0 && diff > 0)
  43                 xh = hi - 1;
  44               else if (xl > 0 && diff < 0)
  45                 xh = hi + 1;
  46               else
  47                 xh = hi;
  48             }
  49           else
  50             xh = hi;
  51           xl = 0;
  52         }
  53       else
  54         {
  55           /* The high part is a nonzero integer.  Rounding the low
  56              part to nearest, ties round to even, is always correct,
  57              as a high part that is an odd integer together with a low
  58              part with magnitude 0.5 is not a valid long double.  */
  59           xl = __roundeven (xl);
  60           xh = hi;
  61           ldbl_canonicalize_int (&xh, &xl);
  62         }
  63     }
  64   else
  65     /* Quiet signaling NaN arguments.  */
  66     xh += xh;
  67
  68   return ldbl_pack (xh, xl);
  69 }
  70 weak_alias (__roundevenl, roundevenl)