1 /* __gmpfr_floor_log2 - returns floor(log(d)/log(2)) 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. 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 http://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 #include "mpfr-impl.h" 24 25 /* returns floor(log2(d)) */ 26 long 27 __gmpfr_floor_log2 (double d) 28 { 29 #if _GMP_IEEE_FLOATS 30 union ieee_double_extract x; 31 32 x.d = d; 33 return (long) x.s.exp - 1023; 34 #else 35 long exp; 36 double m; 37 38 MPFR_ASSERTD (d >= 0); 39 if (d >= 1.0) 40 { 41 exp = -1; 42 for( m= 1.0 ; m <= d ; m *=2.0 ) 43 exp++; 44 } 45 else 46 { 47 exp = 0; 48 for( m= 1.0 ; m > d ; m *= (1.0/2.0) ) 49 exp--; 50 } 51 return exp; 52 #endif 53 } 54