1  /* mpfr_powerof2_raw -- test whether a floating-point number is a power of 2
       2  
       3  Copyright 2002-2023 Free Software Foundation, Inc.
       4  Contributed by the AriC and Caramba 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  https://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    /* This is an internal function, and we may call it with some
      35       wrong numbers (ie good mantissa but wrong flags or exp)
      36       So we don't want to test if it is a pure FP.
      37       MPFR_ASSERTN(MPFR_IS_PURE_FP(x)); */
      38    return mpfr_powerof2_raw2 (MPFR_MANT(x), MPFR_LIMB_SIZE(x));
      39  }
      40  
      41  int
      42  mpfr_powerof2_raw2 (const mp_limb_t *xp, mp_size_t xn)
      43  {
      44    if (xp[--xn] != MPFR_LIMB_HIGHBIT)
      45      return 0;
      46    while (xn > 0)
      47      if (xp[--xn] != 0)
      48        return 0;
      49    return 1;
      50  }