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/* mpn_sub_n -- Subtract two limb vectors of equal, non-zero length.

Copyright (C) 1992, 1993, 1994, 1996 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 2.1 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; see the file COPYING.LIB.  If not, write to

the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,

MA 02111-1307, USA. */

#include <config.h>

#include "gmp-impl.h"

mp_limb_t

#if __STDC__

mpn_sub_n (mp_ptr res_ptr, mp_srcptr s1_ptr, mp_srcptr s2_ptr, mp_size_t size)

#else

mpn_sub_n (res_ptr, s1_ptr, s2_ptr, size)

     register mp_ptr res_ptr;

     register mp_srcptr s1_ptr;

     register mp_srcptr s2_ptr;

     mp_size_t size;

#endif

{

  register mp_limb_t x, y, cy;

  register mp_size_t j;

  /* The loop counter and index J goes from -SIZE to -1.  This way

     the loop becomes faster.  */

  j = -size;

  /* Offset the base pointers to compensate for the negative indices.  */

  s1_ptr -= j;

  s2_ptr -= j;

  res_ptr -= j;

  cy = 0;

  do

    {

      y = s2_ptr[j];

      x = s1_ptr[j];

      y += cy;                  /* add previous carry to subtrahend */

      cy = (y < cy);            /* get out carry from that addition */

      y = x - y;                /* main subtract */

      cy = (y > x) + cy;        /* get out carry from the subtract, combine */

      res_ptr[j] = y;

    }

  while (++j != 0);

  return cy;

}