1 /* __gmpfr_ceil_log2 - returns ceil(log(d)/log(2))
3 Copyright 1999, 2000, 2001, 2002, 2003, 2004, 2006, 2007, 2008, 2009, 2010, 2011 Free Software Foundation, Inc.
4 Contributed by the Arenaire and Caramel projects, INRIA.
6 This file is part of the GNU MPFR Library.
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.
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.
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 http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
21 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
23 #include "mpfr-impl.h"
25 /* returns ceil(log(d)/log(2)) if d > 0,
27 and floor(log(-d)/log(2))+1 if d < 0*/
29 __gmpfr_ceil_log2 (double d)
33 union ieee_double_extract x;
37 x.s.exp = 1023; /* value for 1 <= d < 2 */
38 if (x.d != 1.0) /* d: not a power of two? */
45 return __gmpfr_floor_log2(-d)+1;
51 for( m= 1.0 ; m < d ; m *=2.0 )
57 for( m= 1.0 ; m >= d ; m *= (1.0/2.0) )