sysdeps/ieee754/dbl-64/s_llrint.c

   1 /* Round argument to nearest integral value according to current rounding
   2    direction.
   3    Copyright (C) 1997-2014 Free Software Foundation, Inc.
   4    This file is part of the GNU C Library.
   5    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
   6
   7    The GNU C Library is free software; you can redistribute it and/or
   8    modify it under the terms of the GNU Lesser General Public
   9    License as published by the Free Software Foundation; either
  10    version 2.1 of the License, or (at your option) any later version.
  11
  12    The GNU C Library is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15    Lesser General Public License for more details.
  16
  17    You should have received a copy of the GNU Lesser General Public
  18    License along with the GNU C Library; if not, see
  19    <http://www.gnu.org/licenses/>.  */
  20
  21 #include <math.h>
  22
  23 #include <math_private.h>
  24
  25 static const double two52[2] =
  26 {
  27   4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
  28  -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
  29 };
  30
  31
  32 long long int
  33 __llrint (double x)
  34 {
  35   int32_t j0;
  36   u_int32_t i1, i0;
  37   long long int result;
  38   volatile double w;
  39   double t;
  40   int sx;
  41
  42   EXTRACT_WORDS (i0, i1, x);
  43   j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
  44   sx = i0 >> 31;
  45   i0 &= 0xfffff;
  46   i0 |= 0x100000;
  47
  48   if (j0 < 20)
  49     {
  50       w = two52[sx] + x;
  51       t = w - two52[sx];
  52       EXTRACT_WORDS (i0, i1, t);
  53       j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
  54       i0 &= 0xfffff;
  55       i0 |= 0x100000;
  56
  57       result = (j0 < 0 ? 0 : i0 >> (20 - j0));
  58     }
  59   else if (j0 < (int32_t) (8 * sizeof (long long int)) - 1)
  60     {
  61       if (j0 >= 52)
  62         result = (((long long int) i0 << 32) | i1) << (j0 - 52);
  63       else
  64         {
  65           w = two52[sx] + x;
  66           t = w - two52[sx];
  67           EXTRACT_WORDS (i0, i1, t);
  68           j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
  69           i0 &= 0xfffff;
  70           i0 |= 0x100000;
  71
  72           if (j0 == 20)
  73             result = (long long int) i0;
  74           else
  75             result = ((long long int) i0 << (j0 - 20)) | (i1 >> (52 - j0));
  76         }
  77     }
  78   else
  79     {
  80       /* The number is too large.  It is left implementation defined
  81          what happens.  */
  82       return (long long int) x;
  83     }
  84
  85   return sx ? -result : result;
  86 }
  87
  88 weak_alias (__llrint, llrint)
  89 #ifdef NO_LONG_DOUBLE
  90 strong_alias (__llrint, __llrintl)
  91 weak_alias (__llrint, llrintl)
  92 #endif