1/* __gmpfr_floor_log2 - returns floor(log(d)/log(2)) 2 3Copyright 1999-2004, 2006-2023 Free Software Foundation, Inc. 4Contributed by the AriC and Caramba 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 20https://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 floor(log2(d)) */ 26long 27__gmpfr_floor_log2 (double d) 28{ 29 long exp; 30#if _MPFR_IEEE_FLOATS 31 union mpfr_ieee_double_extract x; 32 33 x.d = d; 34 /* The cast below is useless in theory, but let us not depend on the 35 integer promotion rules (for instance, tcc is currently wrong). */ 36 exp = (long) x.s.exp - 1023; 37 MPFR_ASSERTN (exp < 1023); /* fail on infinities */ 38 return exp; 39#else /* _MPFR_IEEE_FLOATS */ 40 double m; 41 42 MPFR_ASSERTD (d >= 0); 43 if (d >= 1.0) 44 { 45 exp = -1; 46 for (m = 1.0; m <= d; m *= 2.0) 47 exp++; 48 } 49 else 50 { 51 exp = 0; 52 for (m = 1.0; m > d; m *= 0.5) 53 exp--; 54 } 55 return exp; 56#endif /* _MPFR_IEEE_FLOATS */ 57} 58