sysdeps/ieee754/dbl-64/s_llrint.c

   1 /* Round argument to nearest integral value according to current rounding
   2    direction.
   3    Copyright (C) 1997, 2004, 2006 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, write to the Free
  19    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  20    02111-1307 USA.  */
  21
  22 #include <math.h>
  23
  24 #include "math_private.h"
  25
  26 static const double two52[2] =
  27 {
  28   4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
  29  -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
  30 };
  31
  32
  33 long long int
  34 __llrint (double x)
  35 {
  36   int32_t j0;
  37   u_int32_t i1, i0;
  38   long long int result;
  39   volatile double w;
  40   double t;
  41   int sx;
  42
  43   EXTRACT_WORDS (i0, i1, x);
  44   j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
  45   sx = i0 >> 31;
  46   i0 &= 0xfffff;
  47   i0 |= 0x100000;
  48
  49   if (j0 < 20)
  50     {
  51       w = two52[sx] + x;
  52       t = w - two52[sx];
  53       EXTRACT_WORDS (i0, i1, t);
  54       j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
  55       i0 &= 0xfffff;
  56       i0 |= 0x100000;
  57
  58       result = (j0 < 0 ? 0 : i0 >> (20 - j0));
  59     }
  60   else if (j0 < (int32_t) (8 * sizeof (long long int)) - 1)
  61     {
  62       if (j0 >= 52)
  63         result = (((long long int) i0 << 32) | i1) << (j0 - 52);
  64       else
  65         {
  66           w = two52[sx] + x;
  67           t = w - two52[sx];
  68           EXTRACT_WORDS (i0, i1, t);
  69           j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
  70           i0 &= 0xfffff;
  71           i0 |= 0x100000;
  72
  73           if (j0 == 20)
  74             result = (long long int) i0;
  75           else
  76             result = ((long long int) i0 << (j0 - 20)) | (i1 >> (52 - j0));
  77         }
  78     }
  79   else
  80     {
  81       /* The number is too large.  It is left implementation defined
  82          what happens.  */
  83       return (long long int) x;
  84     }
  85
  86   return sx ? -result : result;
  87 }
  88
  89 weak_alias (__llrint, llrint)
  90 #ifdef NO_LONG_DOUBLE
  91 strong_alias (__llrint, __llrintl)
  92 weak_alias (__llrint, llrintl)
  93 #endif