/* 
    Copyright (C) 2009, 2011 William Hart

    This file is part of FLINT.

    FLINT is free software: you can redistribute it and/or modify it under
    the terms of the GNU Lesser General Public License (LGPL) as published
    by the Free Software Foundation; either version 2.1 of the License, or
    (at your option) any later version.  See <https://www.gnu.org/licenses/>.
*/

#include "gmp.h"
#include "flint.h"
#include "fft.h"

void mpn_normmod_2expp1(mp_limb_t * t, mp_size_t limbs)
{
   mp_limb_signed_t hi = t[limbs];
   
   if (hi)
   {
      t[limbs] = 0;

      mpn_addmod_2expp1_1(t, limbs, -hi);

      /* hi will now be in [-1,1] */
      if ((hi = t[limbs]))
      {
         t[limbs] = 0;

         mpn_addmod_2expp1_1(t, limbs, -hi);

         if (t[limbs] == ~(mp_limb_signed_t) 0) /* if we now have -1 (very unlikely) */
         {
            t[limbs] = 0;
            mpn_addmod_2expp1_1(t, limbs, 1);            
         }
      }
   }
}