mpir/mpn/generic/divrem_hensel_rsh_qr_1.c

/*
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_divrem_hensel_rsh_qr_1(mp_ptr qp, mp_srcptr xp, 
                                     mp_size_t n, mp_limb_t d, int s)
{
   mp_size_t j;
   mp_limb_t c, h, q, dummy, h1, t, m;

   ASSERT(n > 0);
   ASSERT(d%2 == 1);
   ASSERT_MPN(xp, n);
   ASSERT(MPN_SAME_OR_SEPARATE_P(qp, xp, n));
   ASSERT(s >= 0);
   
   modlimb_invert(m, d); /* should we allow s=0 ?? */

   c = 0;
   h = 0;
   t = 0;

   for (j = 0; j <= n - 2; j++)
   {
      h1 = (xp[j]>>s) | (xp[j + 1]<<(GMP_LIMB_BITS - 1 - s)<<1);
      t = h + c;
      
      if (t > h1)
      {
         h1 = h1 - t;
         c = 1;
      }
      else
      {
         h1 = h1 - t;
         c = 0;
      }
    
      q = h1*m;
      qp[j] = q;
      umul_ppmm(h, dummy, q, d);
      ASSERT(dummy == h1);
   }

   h1 = xp[n - 1]>>s;
   t = h + c;
   
   if (t > h1)
   {
      h1 = h1 - t;
      c = 1;
   }
   else
   {
      h1 = h1 - t;
      c = 0;
   }

   q = h1*m;
   qp[n - 1] = q;
   umul_ppmm(h, dummy, q, d);

   ASSERT(dummy == h1);

   return h + c;
}