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, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    02111-1307 USA.  */
  20
  21 #include <math.h>
  22
  23 #include "math_private.h"
  24
  25
  26 static const double huge = 1.0e300;
  27
  28 double
  29 round (double x)
  30 {
  31   int32_t i0, j0;
  32   u_int32_t i1;
  33
  34   EXTRACT_WORDS (i0, i1, x);
  35   j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
  36   if (j0 < 20)
  37     {
  38       if (j0 < 0)
  39         {
  40           if (huge + x > 0.0)
  41             {
  42               i0 &= 0x80000000;
  43               if (j0 == -1)
  44                 i0 |= 0x3ff00000;
  45               i1 = 0;
  46             }
  47         }
  48       else
  49         {
  50           u_int32_t i = 0x000fffff >> j0;
  51           if (((i0 & i) | i1) == 0)
  52             /* X is integral.  */
  53             return x;
  54           if (huge + x > 0.0)
  55             {
  56               /* Raise inexact if x != 0.  */
  57               i0 += 0x00080000 >> j0;
  58               i0 &= ~i;
  59               i1 = 0;
  60             }
  61         }
  62     }
  63   else if (j0 > 51)
  64     {
  65       if (j0 == 0x400)
  66         /* Inf or NaN.  */
  67         return x + x;
  68       else
  69         return x;
  70     }
  71   else
  72     {
  73       u_int32_t i = 0xffffffff >> (j0 - 20);
  74       if ((i1 & i) == 0)
  75         /* X is integral.  */
  76         return x;
  77
  78       if (huge + x > 0.0)
  79         {
  80           /* Raise inexact if x != 0.  */
  81           u_int32_t j = i1 + (1 << (51 - j0));
  82           if (j < i1)
  83             i0 += 1;
  84           i1 = j;
  85         }
  86       i1 &= ~i;
  87     }
  88
  89   INSERT_WORDS (x, i0, i1);
  90   return x;
  91 }
  92 libm_hidden_def(round)