libm/s_lrint.c

   1 /* Round argument to nearest integral value according to current rounding
   2    direction.
   3    Copyright (C) 1997, 2004 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 <features.h>
  22 /* Prevent math.h from defining a colliding inline */
  23 #undef __USE_EXTERN_INLINES
  24 #include <math.h>
  25 #include "math_private.h"
  26
  27 static const double two52[2] =
  28 {
  29   4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
  30  -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
  31 };
  32
  33
  34 long int
  35 lrint (double x)
  36 {
  37   int32_t _j0;
  38   u_int32_t i0,i1;
  39   volatile double w;
  40   double t;
  41   long int result;
  42   int sx;
  43
  44   EXTRACT_WORDS (i0, i1, x);
  45   _j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
  46   sx = i0 >> 31;
  47   i0 &= 0xfffff;
  48   i0 |= 0x100000;
  49
  50   if (_j0 < 20)
  51     {
  52       w = two52[sx] + x;
  53       t = w - two52[sx];
  54       EXTRACT_WORDS (i0, i1, t);
  55       _j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
  56       i0 &= 0xfffff;
  57       i0 |= 0x100000;
  58       result = (_j0 < 0 ? 0 : i0 >> (20 - _j0));
  59     }
  60   else if (_j0 < (int32_t) (8 * sizeof (long int)) - 1)
  61     {
  62       if (_j0 >= 52)
  63         result = ((long int) i0 << (_j0 - 20)) | (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 int) i0;
  75           else
  76             result = ((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 int) x;
  84     }
  85
  86   return sx ? -result : result;
  87 }
  88 libm_hidden_def(lrint)