/* mpn_gcd_11 -- limb greatest common divisor.

Copyright 1994, 1996, 2000, 2001, 2009, 2012, 2019 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"

mp_limb_t

mpn_gcd_11 (mp_limb_t u, mp_limb_t v)

{

  ASSERT (u & v & 1);

  /* In this loop, we represent the odd numbers ulimb and vlimb

     without the redundant least significant one bit. This reduction

     in size by one bit ensures that the high bit of t, below, is set

     if and only if vlimb > ulimb. */

  u >>= 1;

  v >>= 1;

  while (u != v)

    {

      mp_limb_t t;

      mp_limb_t vgtu;

      int c;

      t = u - v;

      vgtu = LIMB_HIGHBIT_TO_MASK (t);

      /* v <-- min (u, v) */

      v += (vgtu & t);

      /* u <-- |u - v| */

      u = (t ^ vgtu) - vgtu;

      count_trailing_zeros (c, t);

      /* We have c <= GMP_LIMB_BITS - 2 here, so that

     ulimb >>= (c + 1);

   would be safe. But unlike the addition c + 1, a separate

   shift by 1 is independent of c, and can be executed in

   parallel with count_trailing_zeros. */

      u = (u >> 1) >> c;

    }

  return (u << 1) + 1;

}