/* __gmpfr_floor_log2 - returns floor(log(d)/log(2)) Copyright 1999-2004, 2006-2023 Free Software Foundation, Inc. Contributed by the AriC and Caramba projects, INRIA. This file is part of the GNU MPFR Library. The GNU MPFR Library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version. The GNU MPFR Library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with the GNU MPFR Library; see the file COPYING.LESSER. If not, see https://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */ #include "mpfr-impl.h" /* returns floor(log2(d)) */ long __gmpfr_floor_log2 (double d) { long exp; #if _MPFR_IEEE_FLOATS union mpfr_ieee_double_extract x; x.d = d; /* The cast below is useless in theory, but let us not depend on the integer promotion rules (for instance, tcc is currently wrong). */ exp = (long) x.s.exp - 1023; MPFR_ASSERTN (exp < 1023); /* fail on infinities */ return exp; #else /* _MPFR_IEEE_FLOATS */ double m; MPFR_ASSERTD (d >= 0); if (d >= 1.0) { exp = -1; for (m = 1.0; m <= d; m *= 2.0) exp++; } else { exp = 0; for (m = 1.0; m > d; m *= 0.5) exp--; } return exp; #endif /* _MPFR_IEEE_FLOATS */ } |