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Initial revision

/* mpn_gcd_1 --

Copyright (C) 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 Library General Public License as published by
the Free Software Foundation; either version 2 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 Library General Public
License for more details.

You should have received a copy of the GNU Library 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 "gmp.h"
#include "gmp-impl.h"
#include "longlong.h"

/* Does not work for U == 0 or V == 0.  It would be tough to make it work for
   V == 0 since gcd(x,0) = x, and U does not generally fit in an mp_limb_t.  */

mp_limb_t
mpn_gcd_1 (up, size, vlimb)
     mp_srcptr up;
     mp_size_t size;
     mp_limb_t vlimb;
{
  mp_limb_t ulimb;
  unsigned long int u_low_zero_bits, v_low_zero_bits;

  if (size > 1)
    {
      ulimb = mpn_mod_1 (up, size, vlimb);
      if (ulimb == 0)
	return vlimb;
    }
  else
    ulimb = up[0];

  /*  Need to eliminate low zero bits.  */
  count_trailing_zeros (u_low_zero_bits, ulimb);
  ulimb >>= u_low_zero_bits;

  count_trailing_zeros (v_low_zero_bits, vlimb);
  vlimb >>= v_low_zero_bits;

  while (ulimb != vlimb)
    {
      if (ulimb > vlimb)
	{
	  ulimb -= vlimb;
	  do
	    ulimb >>= 1;
	  while ((ulimb & 1) == 0);
	}
      else /*  vlimb > ulimb.  */
	{
	  vlimb -= ulimb;
	  do
	    vlimb >>= 1;
	  while ((vlimb & 1) == 0);
	}
    }

  return  ulimb << MIN (u_low_zero_bits, v_low_zero_bits);
}