libm/s_llround.c

   1 /* Round double value to long long int.
   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 long long int
  24 llround (double x)
  25 {
  26   int32_t _j0;
  27   u_int32_t i1, i0;
  28   long long int result;
  29   int sign;
  30
  31   EXTRACT_WORDS (i0, i1, x);
  32   _j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
  33   sign = (i0 & 0x80000000) != 0 ? -1 : 1;
  34   i0 &= 0xfffff;
  35   i0 |= 0x100000;
  36
  37   if (_j0 < 20)
  38     {
  39       if (_j0 < 0)
  40         return _j0 < -1 ? 0 : sign;
  41       else
  42         {
  43           i0 += 0x80000 >> _j0;
  44
  45           result = i0 >> (20 - _j0);
  46         }
  47     }
  48   else if (_j0 < (int32_t) (8 * sizeof (long long int)) - 1)
  49     {
  50       if (_j0 >= 52)
  51         result = (((long long int) i0 << 32) | i1) << (_j0 - 52);
  52       else
  53         {
  54           u_int32_t j = i1 + (0x80000000 >> (_j0 - 20));
  55           if (j < i1)
  56             ++i0;
  57
  58           if (_j0 == 20)
  59             result = (long long int) i0;
  60           else
  61             result = ((long long int) i0 << (_j0 - 20)) | (j >> (52 - _j0));
  62         }
  63     }
  64   else
  65     {
  66       /* The number is too large.  It is left implementation defined
  67          what happens.  */
  68       return (long long int) x;
  69     }
  70
  71   return sign * result;
  72 }
  73 libm_hidden_def(llround)