gcc/mpfr/powerof2.c

/* mpfr_powerof2_raw -- test whether a floating-point number is a power of 2

Copyright 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
Contributed by the Arenaire and Cacao 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 2.1 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.LIB.  If not, write to
the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,
MA 02110-1301, USA. */

#include "mpfr-impl.h"

/* This is an internal function and one assumes that x is a real number. */

int
mpfr_powerof2_raw (mpfr_srcptr x)
{
  mp_limb_t *xp;
  mp_size_t xn;

  /* This is an internal function, and we may call it with some
     wrong numbers (ie good mantissa but wrong flags or exp)
     So we don't want to test if it is a pure FP.
     MPFR_ASSERTN(MPFR_IS_PURE_FP(x)); */
  xp = MPFR_MANT(x);
  xn = (MPFR_PREC(x) - 1) / BITS_PER_MP_LIMB;
  /*if (NOT_POW2(xp[xn]))*/
  if (xp[xn] != MPFR_LIMB_HIGHBIT)
    return 0;
  while (xn > 0)
    if (xp[--xn] != 0)
      return 0;
  return 1;
}