/* mpn_mul -- Multiply two natural numbers.

Copyright (C) 1991 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 General Public License as published by
the Free Software Foundation; either version 1, 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 General Public License for more details.

You should have received a copy of the GNU General Public License
along with the GNU MP Library; see the file COPYING.  If not, write to
the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */

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

/* Multiply the natural numbers u (pointed to by UP, with USIZE limbs)
   and v (pointed to by VP, with VSIZE limbs), and store the result at
   PRODP.  USIZE + VSIZE limbs are always stored, but if the input
   operands are normalized, the return value will reflect the true
   result size (which is either USIZE + VSIZE, or USIZE + VSIZE -1).

   NOTE: The space pointed to by PRODP is overwritten before finished
   with U and V, so overlap is an error.

   Argument constraints:
   1. USIZE >= VSIZE.
   2. PRODP != UP and PRODP != VP, i.e. the destination
      must be distinct from the multiplier and the multiplicand.  */

mp_size_t
mpn_mul_classic (mp_ptr prodp,
		  mp_srcptr up, mp_size_t usize,
		  mp_srcptr vp, mp_size_t vsize)
{
  mp_size_t n;
  mp_size_t prod_size;
  mp_limb cy;
  int i, j;
  mp_limb prod_low, prod_high;
  mp_limb cy_dig;
  mp_limb v_limb, c;

  if (vsize == 0)
    return 0;

  /* Offset UP and PRODP so that the inner loop can be faster.  */
  up += usize;
  prodp += usize;

  /* Multiply by the first limb in V separately, as the result can
     be stored (not added) to PROD.  We also avoid a loop for zeroing.  */
  v_limb = vp[0];
  cy_dig = 0;
  j = -usize;
  do
    {
      umul_ppmm (prod_high, prod_low, up[j], v_limb);
      add_ssaaaa (cy_dig, prodp[j], prod_high, prod_low, 0, cy_dig);
      j++;
    }
  while (j < 0);

  prodp[j] = cy_dig;
  prodp++;

  /* For each iteration in the outer loop, multiply one limb from
     U with one limb from V, and add it to PROD.  */
  for (i = 1; i < vsize; i++)
    {
      v_limb = vp[i];
      cy_dig = 0;
      j = -usize;

      /* Inner loops.  Simulate the carry flag by jumping between
	 these loops.  The first is used when there was no carry
	 in the previois iteration; the second when there was carry.  */

      do
	{
	  umul_ppmm (prod_high, prod_low, up[j], v_limb);
	  add_ssaaaa (cy_dig, prod_low, prod_high, prod_low, 0, cy_dig);
	  c = prodp[j];
	  prod_low += c;
	  prodp[j] = prod_low;
	  if (prod_low < c)
	    goto cy_loop;
	ncy_loop:
	  j++;
	}
      while (j < 0);

      prodp[j] = cy_dig;
      prodp++;
      continue;

      do
	{
	  umul_ppmm (prod_high, prod_low, up[j], v_limb);
	  add_ssaaaa (cy_dig, prod_low, prod_high, prod_low, 0, cy_dig);
	  c = prodp[j];
	  prod_low += c + 1;
	  prodp[j] = prod_low;
	  if (prod_low > c)
	    goto ncy_loop;
	cy_loop:
	  j++;
	}
      while (j < 0);

      cy_dig += 1;
      prodp[j] = cy_dig;
      prodp++;
    }

  return usize + vsize - (cy_dig == 0);
}