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Diffstat (limited to 'src/ufloor_log2.c')
-rw-r--r-- | src/ufloor_log2.c | 53 |
1 files changed, 53 insertions, 0 deletions
diff --git a/src/ufloor_log2.c b/src/ufloor_log2.c new file mode 100644 index 0000000..9200dbf --- /dev/null +++ b/src/ufloor_log2.c @@ -0,0 +1,53 @@ +/* __gmpfr_floor_log2 - returns floor(log(d)/log(2)) + +Copyright 1999, 2000, 2001, 2002, 2003, 2004, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Free Software Foundation, Inc. +Contributed by the AriC and Caramel 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 +http://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) +{ +#if _GMP_IEEE_FLOATS + union ieee_double_extract x; + + x.d = d; + return (long) x.s.exp - 1023; +#else + long exp; + 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 *= (1.0/2.0) ) + exp--; + } + return exp; +#endif +} |