/* mpn_toom_eval_pm2rexp -- Evaluate a polynomial in +2^-k and -2^-k

   Contributed to the GNU project by Marco Bodrato

   THE FUNCTION IN THIS FILE IS INTERNAL WITH A MUTABLE INTERFACE.  IT IS ONLY
   SAFE TO REACH IT THROUGH DOCUMENTED INTERFACES.  IN FACT, IT IS ALMOST
   GUARANTEED THAT IT WILL CHANGE OR DISAPPEAR IN A FUTURE GNU MP RELEASE.

Copyright 2009 Free Software Foundation, Inc.

This file is part of the GNU MP Library.

The GNU MP 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 3 of the License, or (at your
option) any later version.

The GNU MP 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 MP Library.  If not, see http://www.gnu.org/licenses/.  */


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

#if HAVE_NATIVE_mpn_addlsh_n
#define DO_mpn_addlsh_n(dst,src,n,s,ws) mpn_addlsh_n(dst,dst,src,n,s)
#else
static mp_limb_t
DO_mpn_addlsh_n(mp_ptr dst, mp_srcptr src, mp_size_t n, unsigned int s, mp_ptr ws)
{
#if USE_MUL_1 && 0
  return mpn_addmul_1(dst,src,n,CNST_LIMB(1) <<(s));
#else
  mp_limb_t __cy;
  __cy = mpn_lshift(ws,src,n,s);
  return    __cy + mpn_add_n(dst,dst,ws,n);
#endif
}
#endif

/* Evaluates a polynomial of degree k >= 3. */
int
mpn_toom_eval_pm2rexp (mp_ptr rp, mp_ptr rm,
		      unsigned int q, mp_srcptr ap, mp_size_t n, mp_size_t t,
		      unsigned int s, mp_ptr ws)
{
  unsigned int i;
  int neg;
  /* {ap,q*n+t} -> {rp,n+1} {rm,n+1} , with {ws, n+1}*/
  ASSERT (n >= t);
  ASSERT (s != 0); /* or _eval_pm1 should be used */
  ASSERT (q > 1);
  ASSERT (s*q < GMP_NUMB_BITS);
  rp[n] = mpn_lshift(rp, ap, n, s*q);
  ws[n] = mpn_lshift(ws, ap+n, n, s*(q-1));
  if( (q & 1) != 0) {
    ASSERT_NOCARRY(mpn_add(ws,ws,n+1,ap+n*q,t));
    rp[n] += DO_mpn_addlsh_n(rp, ap+n*(q-1), n, s, rm);
  } else {
    ASSERT_NOCARRY(mpn_add(rp,rp,n+1,ap+n*q,t));
  }
  for(i=2; i<q-1; i++)
  {
    rp[n] += DO_mpn_addlsh_n(rp, ap+n*i, n, s*(q-i), rm);
    i++;
    ws[n] += DO_mpn_addlsh_n(ws, ap+n*i, n, s*(q-i), rm);
  };

  neg = (mpn_cmp (rp, ws, n + 1) < 0) ? ~0 : 0;

#if HAVE_NATIVE_mpn_add_n_sub_n
  if (neg)
    mpn_add_n_sub_n (rp, rm, ws, rp, n + 1);
  else
    mpn_add_n_sub_n (rp, rm, rp, ws, n + 1);
#else /* !HAVE_NATIVE_mpn_add_n_sub_n */
  if (neg)
    mpn_sub_n (rm, ws, rp, n + 1);
  else
    mpn_sub_n (rm, rp, ws, n + 1);

  ASSERT_NOCARRY (mpn_add_n (rp, rp, ws, n + 1));
#endif /* !HAVE_NATIVE_mpn_add_n_sub_n */

  return neg;
}
