1 /* __gmpfr_int_ceil_log2 -- Integer ceil of log2(x)
2
3 Copyright 2004-2023 Free Software Foundation, Inc.
4 Contributed by the AriC and Caramba projects, INRIA.
5
6 This file is part of the GNU MPFR Library.
7
8 The GNU MPFR Library is free software; you can redistribute it and/or modify
9 it under the terms of the GNU Lesser General Public License as published by
10 the Free Software Foundation; either version 3 of the License, or (at your
11 option) any later version.
12
13 The GNU MPFR Library is distributed in the hope that it will be useful, but
14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
15 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
16 License for more details.
17
18 You should have received a copy of the GNU Lesser General Public License
19 along with the GNU MPFR Library; see the file COPYING.LESSER. If not, see
20 https://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
21 51 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
26 int
__gmpfr_int_ceil_log2(unsigned long n)27 __gmpfr_int_ceil_log2 (unsigned long n)
28 {
29 if (MPFR_UNLIKELY (n == 1))
30 return 0;
31 else
32 #ifdef MPFR_LONG_WITHIN_LIMB
33 {
34 int b;
35 mp_limb_t limb;
36
37 MPFR_ASSERTN (n > 1);
38 limb = n - 1;
39 MPFR_ASSERTN (limb == n - 1);
40 count_leading_zeros (b, limb);
41 b = GMP_NUMB_BITS - b;
42 MPFR_ASSERTD (b >= 0);
43 return b;
44 }
45 #else
46 return mpfr_nbits_ulong (n - 1);
47 #endif
48 }
49