1/* __gmpfr_ceil_exp2 - returns y >= 2^d
2
3Copyright 1999, 2000, 2001, 2002, 2003, 2004, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Free Software Foundation, Inc.
4Contributed by the AriC and Caramel projects, INRIA.
5
6This file is part of the GNU MPFR Library.
7
8The GNU MPFR Library is free software; you can redistribute it and/or modify
9it under the terms of the GNU Lesser General Public License as published by
10the Free Software Foundation; either version 3 of the License, or (at your
11option) any later version.
12
13The GNU MPFR Library is distributed in the hope that it will be useful, but
14WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
15or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
16License for more details.
17
18You should have received a copy of the GNU Lesser General Public License
19along with the GNU MPFR Library; see the file COPYING.LESSER.  If not, see
20http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
2151 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
22
23#include "mpfr-impl.h"
24
25/* returns y >= 2^d, assuming that d <= 1024
26   for d integer, returns exactly 2^d
27*/
28double
29__gmpfr_ceil_exp2 (double d)
30{
31  long exp;
32#if _GMP_IEEE_FLOATS
33  union ieee_double_extract x;
34#else
35  struct {double d;} x;
36#endif
37
38  MPFR_ASSERTN(d <= 1024.0);
39  exp = (long) d;
40  if (d != (double) exp)
41    exp++;
42  /* now exp = ceil(d) */
43  x.d = 1.0;
44#if _GMP_IEEE_FLOATS
45  x.s.exp = exp <= -1022 ? 1 : 1023 + exp;
46#else
47  if (exp >= 0)
48    {
49      while (exp != 0)
50        {
51          x.d *= 2.0;
52          exp--;
53        }
54    }
55  else
56    {
57      while (exp != 0)
58        {
59          x.d *= (1.0 / 2.0);
60          exp++;
61        }
62    }
63#endif
64  return x.d;
65}
66