/* mpz_congruent_ui_p -- test congruence of mpz and ulong.

Copyright 2000-2002, 2012 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"

/* There's some explicit checks for c

   application might use that in a test.

   Hopefully the compiler can generate something good for r==(c%d), though

   if modexact is being used exclusively then that's not reached.  */

int

mpz_congruent_ui_p (mpz_srcptr a, unsigned long cu, unsigned long du)

{

  mp_srcptr  ap;

  mp_size_t  asize;

  mp_limb_t  c, d, r;

  if (UNLIKELY (du == 0))

    return (mpz_cmp_ui (a, cu) == 0);

  asize = SIZ(a);

  if (asize == 0)

    {

      if (cu < du)

	return cu == 0;

      else

	return (cu % du) == 0;

    }

  /* For nails don't try to be clever if c or d is bigger than a limb, just

     fake up some mpz_t's and go to the main mpz_congruent_p.  */

  if (du > GMP_NUMB_MAX || cu > GMP_NUMB_MAX)

    {

      mp_limb_t  climbs[2], dlimbs[2];

      mpz_t      cz, dz;

      ALLOC(cz) = 2;

      PTR(cz) = climbs;

      ALLOC(dz) = 2;

      PTR(dz) = dlimbs;

      mpz_set_ui (cz, cu);

      mpz_set_ui (dz, du);

      return mpz_congruent_p (a, cz, dz);

    }

  /* NEG_MOD works on limbs, so convert ulong to limb */

  c = cu;

  d = du;

  if (asize < 0)

    {

      asize = -asize;

      NEG_MOD (c, c, d);

    }

  ap = PTR (a);

  if (ABOVE_THRESHOLD (asize, BMOD_1_TO_MOD_1_THRESHOLD))

    {

      r = mpn_mod_1 (ap, asize, d);

      if (c < d)

	return r == c;

      else

	return r == (c % d);

    }

  if ((d & 1) == 0)

    {

      /* Strip low zero bits to get odd d required by modexact.  If

	 d==e*2^n then a==c mod d if and only if both a==c mod 2^n

	 and a==c mod e.  */

      unsigned	twos;

      if ((ap[0]-c) & LOW_ZEROS_MASK (d))

	return 0;

      count_trailing_zeros (twos, d);

      d >>= twos;

    }

  r = mpn_modexact_1c_odd (ap, asize, d, c);

  return r == 0 || r == d;

}