1/* __gmpfr_int_ceil_log2 -- Integer ceil of log2(x)
2
3Copyright 2004, 2005, 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#define MPFR_NEED_LONGLONG_H /* for count_leading_zeros */
24#include "mpfr-impl.h"
25
26int
27__gmpfr_int_ceil_log2 (unsigned long n)
28{
29  if (MPFR_UNLIKELY (n == 1))
30    return 0;
31  else
32    {
33      int b;
34      mp_limb_t limb;
35
36      MPFR_ASSERTN (n > 1);
37      limb = n - 1;
38      MPFR_ASSERTN (limb == n - 1);
39      count_leading_zeros (b, limb);
40      return GMP_NUMB_BITS - b;
41    }
42}
43