libm/s_round.c

   1 /* Round double to integer away from zero.
   2    Copyright (C) 1997 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 #include "math_private.h"
  22
  23 static const double huge = 1.0e300;
  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           if (huge + x > 0.0)
  38             {
  39               i0 &= 0x80000000;
  40               if (_j0 == -1)
  41                 i0 |= 0x3ff00000;
  42               i1 = 0;
  43             }
  44         }
  45       else
  46         {
  47           u_int32_t i = 0x000fffff >> _j0;
  48           if (((i0 & i) | i1) == 0)
  49             /* X is integral.  */
  50             return x;
  51           if (huge + x > 0.0)
  52             {
  53               /* Raise inexact if x != 0.  */
  54               i0 += 0x00080000 >> _j0;
  55               i0 &= ~i;
  56               i1 = 0;
  57             }
  58         }
  59     }
  60   else if (_j0 > 51)
  61     {
  62       if (_j0 == 0x400)
  63         /* Inf or NaN.  */
  64         return x + x;
  65       else
  66         return x;
  67     }
  68   else
  69     {
  70       u_int32_t i = 0xffffffff >> (_j0 - 20);
  71       if ((i1 & i) == 0)
  72         /* X is integral.  */
  73         return x;
  74
  75       if (huge + x > 0.0)
  76         {
  77           /* Raise inexact if x != 0.  */
  78           u_int32_t j = i1 + (1 << (51 - _j0));
  79           if (j < i1)
  80             i0 += 1;
  81           i1 = j;
  82         }
  83       i1 &= ~i;
  84     }
  85
  86   INSERT_WORDS (x, i0, i1);
  87   return x;
  88 }
  89 libm_hidden_def(round)