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