sysdeps/ieee754/dbl-64/s_round.c

   1 /* Round double to integer away from zero.
   2    Copyright (C) 1997-2017 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 #include <math.h>
  21
  22 #include <math_private.h>
  23
  24
  25 double
  26 __round (double x)
  27 {
  28   int32_t i0, j0;
  29   u_int32_t i1;
  30
  31   EXTRACT_WORDS (i0, i1, x);
  32   j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
  33   if (j0 < 20)
  34     {
  35       if (j0 < 0)
  36         {
  37           i0 &= 0x80000000;
  38           if (j0 == -1)
  39             i0 |= 0x3ff00000;
  40           i1 = 0;
  41         }
  42       else
  43         {
  44           u_int32_t i = 0x000fffff >> j0;
  45           if (((i0 & i) | i1) == 0)
  46             /* X is integral.  */
  47             return x;
  48
  49           i0 += 0x00080000 >> j0;
  50           i0 &= ~i;
  51           i1 = 0;
  52         }
  53     }
  54   else if (j0 > 51)
  55     {
  56       if (j0 == 0x400)
  57         /* Inf or NaN.  */
  58         return x + x;
  59       else
  60         return x;
  61     }
  62   else
  63     {
  64       u_int32_t i = 0xffffffff >> (j0 - 20);
  65       if ((i1 & i) == 0)
  66         /* X is integral.  */
  67         return x;
  68
  69       u_int32_t j = i1 + (1 << (51 - j0));
  70       if (j < i1)
  71         i0 += 1;
  72       i1 = j;
  73       i1 &= ~i;
  74     }
  75
  76   INSERT_WORDS (x, i0, i1);
  77   return x;
  78 }
  79 weak_alias (__round, round)
  80 #ifdef NO_LONG_DOUBLE
  81 strong_alias (__round, __roundl)
  82 weak_alias (__round, roundl)
  83 #endif