/* mpn_divexact_by exact division by (B-1)/f

  Copyright 2009 Jason Moxham

  This file is part of the MPIR Library.

  The MPIR 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 MPIR 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 MPIR Library; see the file COPYING.LIB.  If not, write
  to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  Boston, MA 02110-1301, USA.
*/

#include "mpir.h"
#include "gmp-impl.h"
#include "longlong.h"

mp_limb_t	mpn_divexact_byBm1of(mp_ptr qp,mp_srcptr xp,mp_size_t n,mp_limb_t f,mp_limb_t Bm1of)
{mp_size_t j;mp_limb_t c,acc,ax,dx;

ASSERT(n>0);
ASSERT_MPN(xp,n);
ASSERT(MPN_SAME_OR_SEPARATE_P(qp,xp,n));
ASSERT(Bm1of*f+1==0);
acc=0*Bm1of;// carry in is 0
for(j=0;j<=n-1;j++)
   {umul_ppmm(dx,ax,xp[j],Bm1of);
    SUBC_LIMB(c,acc,acc,ax);
    qp[j]=acc;
    acc-=dx+c;}
// return next quotient*-f    
return acc*-f;}   // so  (xp,n) = (qp,n)*f -ret*B^n    and 0 <= ret < f

// Note the divexact_by3 code is just a special case of this