/* mpz/gcd.c:   Calculate the greatest common divisor of two integers.

Copyright 1991, 1993, 1994, 1996, 2000-2002, 2005, 2010 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.h"

#include "gmp-impl.h"

#include "longlong.h"

void

mpz_gcd (mpz_ptr g, mpz_srcptr u, mpz_srcptr v)

{

  unsigned long int g_zero_bits, u_zero_bits, v_zero_bits;

  mp_size_t g_zero_limbs, u_zero_limbs, v_zero_limbs;

  mp_ptr tp;

  mp_ptr up;

  mp_size_t usize;

  mp_ptr vp;

  mp_size_t vsize;

  mp_size_t gsize;

  TMP_DECL;

  up = PTR(u);

  usize = ABSIZ (u);

  vp = PTR(v);

  vsize = ABSIZ (v);

  /* GCD(0, V) == V.  */

  if (usize == 0)

    {

      SIZ (g) = vsize;

      if (g == v)

	return;

      MPZ_REALLOC (g, vsize);

      MPN_COPY (PTR (g), vp, vsize);

      return;

    }

  /* GCD(U, 0) == U.  */

  if (vsize == 0)

    {

      SIZ (g) = usize;

      if (g == u)

	return;

      MPZ_REALLOC (g, usize);

      MPN_COPY (PTR (g), up, usize);

      return;

    }

  if (usize == 1)

    {

      SIZ (g) = 1;

      PTR (g)[0] = mpn_gcd_1 (vp, vsize, up[0]);

      return;

    }

  if (vsize == 1)

    {

      SIZ(g) = 1;

      PTR (g)[0] = mpn_gcd_1 (up, usize, vp[0]);

      return;

    }

  TMP_MARK;

  /*  Eliminate low zero bits from U and V and move to temporary storage.  */

  while (*up == 0)

    up++;

  u_zero_limbs = up - PTR(u);

  usize -= u_zero_limbs;

  count_trailing_zeros (u_zero_bits, *up);

  tp = up;

  up = TMP_ALLOC_LIMBS (usize);

  if (u_zero_bits != 0)

    {

      mpn_rshift (up, tp, usize, u_zero_bits);

      usize -= up[usize - 1] == 0;

    }

  else

    MPN_COPY (up, tp, usize);

  while (*vp == 0)

    vp++;

  v_zero_limbs = vp - PTR (v);

  vsize -= v_zero_limbs;

  count_trailing_zeros (v_zero_bits, *vp);

  tp = vp;

  vp = TMP_ALLOC_LIMBS (vsize);

  if (v_zero_bits != 0)

    {

      mpn_rshift (vp, tp, vsize, v_zero_bits);

      vsize -= vp[vsize - 1] == 0;

    }

  else

    MPN_COPY (vp, tp, vsize);

  if (u_zero_limbs > v_zero_limbs)

    {

      g_zero_limbs = v_zero_limbs;

      g_zero_bits = v_zero_bits;

    }

  else if (u_zero_limbs < v_zero_limbs)

    {

      g_zero_limbs = u_zero_limbs;

      g_zero_bits = u_zero_bits;

    }

  else  /*  Equal.  */

    {

      g_zero_limbs = u_zero_limbs;

      g_zero_bits = MIN (u_zero_bits, v_zero_bits);

    }

  /*  Call mpn_gcd.  The 2nd argument must not have more bits than the 1st.  */

  vsize = (usize < vsize || (usize == vsize && up[usize-1] < vp[vsize-1]))

    ? mpn_gcd (vp, vp, vsize, up, usize)

    : mpn_gcd (vp, up, usize, vp, vsize);

  /*  Here G <-- V << (g_zero_limbs*GMP_LIMB_BITS + g_zero_bits).  */

  gsize = vsize + g_zero_limbs;

  if (g_zero_bits != 0)

    {

      mp_limb_t cy_limb;

      gsize += (vp[vsize - 1] >> (GMP_NUMB_BITS - g_zero_bits)) != 0;

      MPZ_REALLOC (g, gsize);

      MPN_ZERO (PTR (g), g_zero_limbs);

      tp = PTR(g) + g_zero_limbs;

      cy_limb = mpn_lshift (tp, vp, vsize, g_zero_bits);

      if (cy_limb != 0)

	tp[vsize] = cy_limb;

    }

  else

    {

      MPZ_REALLOC (g, gsize);

      MPN_ZERO (PTR (g), g_zero_limbs);

      MPN_COPY (PTR (g) + g_zero_limbs, vp, vsize);

    }

  SIZ (g) = gsize;

  TMP_FREE;

}