/* Mulder's MulHigh function (short product)

Copyright 2005, 2006 Free Software Foundation, Inc.

This file is part of the MPFR Library.

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

#define MPFR_NEED_LONGLONG_H
#include "mpfr-impl.h"

/* Don't MPFR_MULHIGH_SIZE since it is handled by tuneup */
#ifdef MPFR_MULHIGH_TAB_SIZE
static short mulhigh_ktab[MPFR_MULHIGH_TAB_SIZE];
#else
static short mulhigh_ktab[] = {MPFR_MULHIGH_TAB};
#define MPFR_MULHIGH_TAB_SIZE \
  ((mp_size_t) (sizeof(mulhigh_ktab) / sizeof(mulhigh_ktab[0])))
#endif

/* Put in  rp[n..2n-1] an approximation of the n high limbs
   of {mp, n} * {np, n}.
   The error is at worst of ln(n) for rp[n] and rp[n-1] is totally wrong */
static void
mpfr_mulhigh_n_basecase (mp_ptr rp, mp_srcptr up, mp_srcptr vp, mp_size_t n)
{
  mp_size_t i;

  rp += n-1;
  umul_ppmm (rp[1], rp[0], up[n-1], vp[0]);
  for (i = 1 ; i < n ; i++)
    rp[i+1] = mpn_addmul_1 (rp, up + (n - i - 1), i+1, vp[i]);
}

void
mpfr_mulhigh_n (mp_ptr rp, mp_srcptr np, mp_srcptr mp, mp_size_t n)
{
  mp_size_t k;

  MPFR_ASSERTD (MPFR_MULHIGH_TAB_SIZE > 4);
  k = MPFR_LIKELY (n < MPFR_MULHIGH_TAB_SIZE) ? mulhigh_ktab[n] : 2*n/3;
  MPFR_ASSERTD (k == -1 || k == 0 || (k > n/2 && k < n));
  if (k < 0)
    mpn_mul_basecase (rp, np, n, mp, n);
  else if (k == 0)
    mpfr_mulhigh_n_basecase (rp, np, mp, n);
  else
    {
      mp_size_t l = n - k;
      mp_limb_t cy;

      mpn_mul_n (rp + 2 * l, np + l, mp + l, k); /* fills rp[2l..2n-1] */
      mpfr_mulhigh_n (rp, np + k, mp, l);          /* fills rp[l-1..2l-1] */
      cy = mpn_add_n (rp + n - 1, rp + n - 1, rp + l - 1, l + 1);
      mpfr_mulhigh_n (rp, np, mp + k, l);          /* fills rp[l-1..2l-1] */
      cy += mpn_add_n (rp + n - 1, rp + n - 1, rp + l - 1, l + 1);
      mpn_add_1 (rp + n + l, rp + n + l, k, cy); /* propagate carry */
    }
}

#if 0

#ifdef MPFR_SQRHIGH_TAB_SIZE
static short sqrhigh_ktab[MPFR_SQRHIGH_TAB_SIZE];
#else
static short sqrhigh_ktab[] = {MPFR_SQRHIGH_TAB};
#define MPFR_SQRHIGH_TAB_SIZE (sizeof(sqrhigh_ktab) / sizeof(sqrhigh_ktab[0]))
#endif

void
mpfr_sqrhigh_n (mp_ptr rp, mp_srcptr np, mp_size_t n)
{
  mp_size_t k;

  MPFR_ASSERTD (MPFR_SQRHIGH_TAB_SIZE > 4);
  k = MPFR_LIKELY (n < MPFR_SQRHIGH_TAB_SIZE) ? sqrhigh_ktab[n] : 2*n/3;
  MPFR_ASSERTD (k == -1 || k == 0 || (k > n/2 && k < n));
  if (k < 0)
    mpn_sqr_basecase (rp, np, n);
  else if (k == 0)
    mpfr_mulhigh_n_basecase (rp, np, np, n);
  else
    {
      mp_size_t l = n - k;
      mp_limb_t cy;

      mpn_sqr_n (rp + 2 * l, np + l, k); /* fills rp[2l..2n-1] */
      mpfr_sqrhigh_n (rp, np + k, l);          /* fills rp[l-1..2l-1] */
      /* FIXME: maybe shift by 2 is a better idea but it has to handle carry*/
      cy = mpn_add_n (rp + n - 1, rp + n - 1, rp + l - 1, l + 1);
      cy += mpn_add_n (rp + n - 1, rp + n - 1, rp + l - 1, l + 1);
      mpn_add_1 (rp + n + l, rp + n + l, k, cy); /* propagate carry */
    }
}

#endif