gcc/gmp/mpz/divis_ui.c

/* mpz_divisible_ui_p -- mpz by ulong divisibility test.

Copyright 2000, 2001, 2002 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 3 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.  If not, see http://www.gnu.org/licenses/.  */

#include "gmp.h"
#include "gmp-impl.h"
#include "longlong.h"


int
mpz_divisible_ui_p (mpz_srcptr a, unsigned long d)
{
  mp_size_t  asize;
  mp_ptr     ap;
  unsigned   twos;

  asize = SIZ(a);
  if (UNLIKELY (d == 0))
    return (asize == 0);

  if (asize == 0)  /* 0 divisible by any d */
    return 1;

  /* For nails don't try to be clever if d is bigger than a limb, just fake
     up an mpz_t and go to the main mpz_divisible_p.  */
  if (d > GMP_NUMB_MAX)
    {
      mp_limb_t  dlimbs[2];
      mpz_t      dz;
      ALLOC(dz) = 2;
      PTR(dz) = dlimbs;
      mpz_set_ui (dz, d);
      return mpz_divisible_p (a, dz);
    }

  ap = PTR(a);
  asize = ABS(asize);  /* ignore sign of a */

  if (BELOW_THRESHOLD (asize, MODEXACT_1_ODD_THRESHOLD))
    return mpn_mod_1 (ap, asize, (mp_limb_t) d) == 0;

  if (! (d & 1))
    {
      /* Strip low zero bits to get odd d required by modexact.  If d==e*2^n
         and a is divisible by 2^n and by e, then it's divisible by d. */

      if ((ap[0] & LOW_ZEROS_MASK (d)) != 0)
        return 0;

      count_trailing_zeros (twos, (mp_limb_t) d);
      d >>= twos;
    }

  return mpn_modexact_1_odd (ap, asize, (mp_limb_t) d) == 0;
}