libm/s_lround.c

   1 /* Round double value to long int.
   2    Copyright (C) 1997, 2004 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 long int
  25 lround (double x)
  26 {
  27   int32_t j0;
  28   u_int32_t i1, i0;
  29   long int result;
  30   int sign;
  31
  32   EXTRACT_WORDS (i0, i1, x);
  33   j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
  34   sign = (i0 & 0x80000000) != 0 ? -1 : 1;
  35   i0 &= 0xfffff;
  36   i0 |= 0x100000;
  37
  38   if (j0 < 20)
  39     {
  40       if (j0 < 0)
  41         return j0 < -1 ? 0 : sign;
  42       else
  43         {
  44           i0 += 0x80000 >> j0;
  45
  46           result = i0 >> (20 - j0);
  47         }
  48     }
  49   else if (j0 < (int32_t) (8 * sizeof (long int)) - 1)
  50     {
  51       if (j0 >= 52)
  52         result = ((long int) i0 << (j0 - 20)) | (i1 << (j0 - 52));
  53       else
  54         {
  55           u_int32_t j = i1 + (0x80000000 >> (j0 - 20));
  56           if (j < i1)
  57             ++i0;
  58
  59           if (j0 == 20)
  60             result = (long int) i0;
  61           else
  62             result = ((long int) i0 << (j0 - 20)) | (j >> (52 - j0));
  63         }
  64     }
  65   else
  66     {
  67       /* The number is too large.  It is left implementation defined
  68          what happens.  */
  69       return (long int) x;
  70     }
  71
  72   return sign * result;
  73 }
  74 libm_hidden_def(lround)