sysdeps/ieee754/dbl-64/s_round.c

   1 /* Round double to integer away from zero.
   2    Copyright (C) 1997-2018 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
   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    <http://www.gnu.org/licenses/>.  */
  19
  20 #define NO_MATH_REDIRECT
  21 #include <math.h>
  22
  23 #include <math_private.h>
  24 #include <libm-alias-double.h>
  25
  26
  27 double
  28 __round (double x)
  29 {
  30   int32_t i0, j0;
  31   uint32_t i1;
  32
  33   EXTRACT_WORDS (i0, i1, x);
  34   j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
  35   if (j0 < 20)
  36     {
  37       if (j0 < 0)
  38         {
  39           i0 &= 0x80000000;
  40           if (j0 == -1)
  41             i0 |= 0x3ff00000;
  42           i1 = 0;
  43         }
  44       else
  45         {
  46           uint32_t i = 0x000fffff >> j0;
  47           if (((i0 & i) | i1) == 0)
  48             /* X is integral.  */
  49             return x;
  50
  51           i0 += 0x00080000 >> j0;
  52           i0 &= ~i;
  53           i1 = 0;
  54         }
  55     }
  56   else if (j0 > 51)
  57     {
  58       if (j0 == 0x400)
  59         /* Inf or NaN.  */
  60         return x + x;
  61       else
  62         return x;
  63     }
  64   else
  65     {
  66       uint32_t i = 0xffffffff >> (j0 - 20);
  67       if ((i1 & i) == 0)
  68         /* X is integral.  */
  69         return x;
  70
  71       uint32_t j = i1 + (1 << (51 - j0));
  72       if (j < i1)
  73         i0 += 1;
  74       i1 = j;
  75       i1 &= ~i;
  76     }
  77
  78   INSERT_WORDS (x, i0, i1);
  79   return x;
  80 }
  81 libm_alias_double (__round, round)