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, write to the Free
  19    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  20    02111-1307 USA.  */
  21
  22 #include <features.h>
  23 /* Prevent math.h from defining a colliding inline */
  24 #undef __USE_EXTERN_INLINES
  25 #include <math.h>
  26 #include "math_private.h"
  27
  28 static const double two52[2] =
  29 {
  30   4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
  31  -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
  32 };
  33
  34
  35 long int
  36 lrint (double x)
  37 {
  38   int32_t j0;
  39   u_int32_t i0,i1;
  40   volatile double w;
  41   double t;
  42   long int result;
  43   int sx;
  44
  45   EXTRACT_WORDS (i0, i1, x);
  46   j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
  47   sx = i0 >> 31;
  48   i0 &= 0xfffff;
  49   i0 |= 0x100000;
  50
  51   if (j0 < 20)
  52     {
  53       if (j0 < -1)
  54         return 0;
  55       else
  56         {
  57           w = two52[sx] + x;
  58           t = w - two52[sx];
  59           EXTRACT_WORDS (i0, i1, t);
  60           j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
  61           i0 &= 0xfffff;
  62           i0 |= 0x100000;
  63
  64           result = i0 >> (20 - j0);
  65         }
  66     }
  67   else if (j0 < (int32_t) (8 * sizeof (long int)) - 1)
  68     {
  69       if (j0 >= 52)
  70         result = ((long int) i0 << (j0 - 20)) | (i1 << (j0 - 52));
  71       else
  72         {
  73           w = two52[sx] + x;
  74           t = w - two52[sx];
  75           EXTRACT_WORDS (i0, i1, t);
  76           j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
  77           i0 &= 0xfffff;
  78           i0 |= 0x100000;
  79
  80           if (j0 == 20)
  81             result = (long int) i0;
  82           else
  83             result = ((long int) i0 << (j0 - 20)) | (i1 >> (52 - j0));
  84         }
  85     }
  86   else
  87     {
  88       /* The number is too large.  It is left implementation defined
  89          what happens.  */
  90       return (long int) x;
  91     }
  92
  93   return sx ? -result : result;
  94 }
  95 libm_hidden_def(lrint)