sysdeps/ieee754/dbl-64/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
  29 double
  30 __round (double x)
  31 {
  32   int32_t i0, j0;
  33   u_int32_t i1;
  34
  35   EXTRACT_WORDS (i0, i1, x);
  36   j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
  37   if (j0 < 20)
  38     {
  39       if (j0 < 0)
  40         {
  41           if (huge + x > 0.0)
  42             {
  43               i0 &= 0x80000000;
  44               if (j0 == -1)
  45                 i0 |= 0x3ff00000;
  46               i1 = 0;
  47             }
  48         }
  49       else
  50         {
  51           u_int32_t i = 0x000fffff >> j0;
  52           if (((i0 & i) | i1) == 0)
  53             /* X is integral.  */
  54             return x;
  55           if (huge + x > 0.0)
  56             {
  57               /* Raise inexact if x != 0.  */
  58               i0 += 0x00080000 >> j0;
  59               i0 &= ~i;
  60               i1 = 0;
  61             }
  62         }
  63     }
  64   else if (j0 > 51)
  65     {
  66       if (j0 == 0x400)
  67         /* Inf or NaN.  */
  68         return x + x;
  69       else
  70         return x;
  71     }
  72   else
  73     {
  74       u_int32_t i = 0xffffffff >> (j0 - 20);
  75       if ((i1 & i) == 0)
  76         /* X is integral.  */
  77         return x;
  78
  79       if (huge + x > 0.0)
  80         {
  81           /* Raise inexact if x != 0.  */
  82           u_int32_t j = i1 + (1 << (51 - j0));
  83           if (j < i1)
  84             i0 += 1;
  85           i1 = j;
  86         }
  87       i1 &= ~i;
  88     }
  89
  90   INSERT_WORDS (x, i0, i1);
  91   return x;
  92 }
  93 weak_alias (__round, round)
  94 #ifdef NO_LONG_DOUBLE
  95 strong_alias (__round, __roundl)
  96 weak_alias (__round, roundl)
  97 #endif