/* mpn_sec_div_qr, mpn_sec_div_r -- Compute Q = floor(U / V), U = U mod V.
   Side-channel silent under the assumption that the used instructions are
   side-channel silent.

   Contributed to the GNU project by Torbjörn Granlund.

Copyright 2011-2015 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 either:

  * 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.

or

  * the GNU General Public License as published by the Free Software
    Foundation; either version 2 of the License, or (at your option) any
    later version.

or both in parallel, as here.

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 General Public License
for more details.

You should have received copies of the GNU General Public License and the
GNU Lesser General Public License along with the GNU MP Library.  If not,
see https://www.gnu.org/licenses/.  */

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

#if OPERATION_sec_div_qr
#define FNAME mpn_sec_div_qr
#define FNAME_itch mpn_sec_div_qr_itch
#define Q(q) q,
#define RETTYPE mp_limb_t
#endif
#if OPERATION_sec_div_r
#define FNAME mpn_sec_div_r
#define FNAME_itch mpn_sec_div_r_itch
#define Q(q)
#define RETTYPE void
#endif

mp_size_t
FNAME_itch (mp_size_t nn, mp_size_t dn)
{
#if OPERATION_sec_div_qr
/* Needs (nn + dn + 1) + mpn_sec_pi1_div_qr's needs of (2nn' - dn + 1) for a
   total of 3nn + 4 limbs at tp.  Note that mpn_sec_pi1_div_qr's nn is one
   greater than ours, therefore +4 and not just +2.  */
  return 3 * nn + 4;
#endif
#if OPERATION_sec_div_r
/* Needs (nn + dn + 1) + mpn_sec_pi1_div_r's needs of (dn + 1) for a total of
   nn + 2dn + 2 limbs at tp.  */
  return nn + 2 * dn + 2;
#endif
}

RETTYPE
FNAME (Q(mp_ptr qp)
       mp_ptr np, mp_size_t nn,
       mp_srcptr dp, mp_size_t dn,
       mp_ptr tp)
{
  mp_limb_t d1, d0;
  unsigned int cnt;
  mp_limb_t inv32;

  ASSERT (dn >= 1);
  ASSERT (nn >= dn);
  ASSERT (dp[dn - 1] != 0);

  d1 = dp[dn - 1];
  count_leading_zeros (cnt, d1);

  if (cnt != 0)
    {
      mp_limb_t qh, cy;
      mp_ptr np2, dp2;
      dp2 = tp;					/* dn limbs */
      mpn_lshift (dp2, dp, dn, cnt);

      np2 = tp + dn;				/* (nn + 1) limbs */
      cy = mpn_lshift (np2, np, nn, cnt);
      np2[nn++] = cy;

      d0 = dp2[dn - 1];
      d0 += (~d0 != 0);
      invert_limb (inv32, d0);

      /* We add nn + dn to tp here, not nn + 1 + dn, as expected.  This is
	 since nn here will have been incremented.  */
#if OPERATION_sec_div_qr
      qh = mpn_sec_pi1_div_qr (np2 + dn, np2, nn, dp2, dn, inv32, tp + nn + dn);
      ASSERT (qh == 0);		/* FIXME: this indicates inefficiency! */
      MPN_COPY (qp, np2 + dn, nn - dn - 1);
      qh = np2[nn - 1];
#else
      mpn_sec_pi1_div_r (np2, nn, dp2, dn, inv32, tp + nn + dn);
#endif

      mpn_rshift (np, np2, dn, cnt);

#if OPERATION_sec_div_qr
      return qh;
#endif
    }
  else
    {
      /* FIXME: Consider copying np => np2 here, adding a 0-limb at the top.
	 That would simplify the underlying pi1 function, since then it could
	 assume nn > dn.  */
      d0 = dp[dn - 1];
      d0 += (~d0 != 0);
      invert_limb (inv32, d0);

#if OPERATION_sec_div_qr
      return mpn_sec_pi1_div_qr (qp, np, nn, dp, dn, inv32, tp);
#else
      mpn_sec_pi1_div_r (np, nn, dp, dn, inv32, tp);
#endif
    }
}
