1 /* mpfr_powerof2_raw -- test whether a floating-point number is a power of 2 2 3 Copyright 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Free Software Foundation, Inc. 4 Contributed by the AriC 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 /* This is an internal function and one assumes that x is a non-special 26 * number (more precisely, only its significand is considered and this 27 * function can be used even if the exponent field of x has not been 28 * initialized). It returns 1 (true) if |x| is a power of 2, else 0. 29 */ 30 31 int 32 mpfr_powerof2_raw (mpfr_srcptr x) 33 { 34 mp_limb_t *xp; 35 mp_size_t xn; 36 37 /* This is an internal function, and we may call it with some 38 wrong numbers (ie good mantissa but wrong flags or exp) 39 So we don't want to test if it is a pure FP. 40 MPFR_ASSERTN(MPFR_IS_PURE_FP(x)); */ 41 xp = MPFR_MANT(x); 42 xn = (MPFR_PREC(x) - 1) / GMP_NUMB_BITS; 43 if (xp[xn] != MPFR_LIMB_HIGHBIT) 44 return 0; 45 while (xn > 0) 46 if (xp[--xn] != 0) 47 return 0; 48 return 1; 49 } 50