contrib/mpfr/powerof2.c

   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 Free Software Foundation, Inc.
   4 Contributed by the Arenaire and Cacao 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 2.1 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.LIB.  If not, write to
  20 the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,
  21 MA 02110-1301, USA. */
  22
  23 #include "mpfr-impl.h"
  24
  25 /* This is an internal function and one assumes that x is a real number. */
  26
  27 int
  28 mpfr_powerof2_raw (mpfr_srcptr x)
  29 {
  30   mp_limb_t *xp;
  31   mp_size_t xn;
  32
  33   /* This is an internal function, and we may call it with some
  34      wrong numbers (ie good mantissa but wrong flags or exp)
  35      So we don't want to test if it is a pure FP.
  36      MPFR_ASSERTN(MPFR_IS_PURE_FP(x)); */
  37   xp = MPFR_MANT(x);
  38   xn = (MPFR_PREC(x) - 1) / BITS_PER_MP_LIMB;
  39   /*if (NOT_POW2(xp[xn]))*/
  40   if (xp[xn] != MPFR_LIMB_HIGHBIT)
  41     return 0;
  42   while (xn > 0)
  43     if (xp[--xn] != 0)
  44       return 0;
  45   return 1;
  46 }