github.com/aergoio/aergo@v1.3.1/libtool/src/gmp-6.1.2/mpz/cong_ui.c (about)

     1  /* mpz_congruent_ui_p -- test congruence of mpz and ulong.
     2  
     3  Copyright 2000-2002, 2012 Free Software Foundation, Inc.
     4  
     5  This file is part of the GNU MP Library.
     6  
     7  The GNU MP Library is free software; you can redistribute it and/or modify
     8  it under the terms of either:
     9  
    10    * the GNU Lesser General Public License as published by the Free
    11      Software Foundation; either version 3 of the License, or (at your
    12      option) any later version.
    13  
    14  or
    15  
    16    * the GNU General Public License as published by the Free Software
    17      Foundation; either version 2 of the License, or (at your option) any
    18      later version.
    19  
    20  or both in parallel, as here.
    21  
    22  The GNU MP Library is distributed in the hope that it will be useful, but
    23  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
    24  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
    25  for more details.
    26  
    27  You should have received copies of the GNU General Public License and the
    28  GNU Lesser General Public License along with the GNU MP Library.  If not,
    29  see https://www.gnu.org/licenses/.  */
    30  
    31  #include "gmp.h"
    32  #include "gmp-impl.h"
    33  #include "longlong.h"
    34  
    35  
    36  /* There's some explicit checks for c<d since it seems reasonably likely an
    37     application might use that in a test.
    38  
    39     Hopefully the compiler can generate something good for r==(c%d), though
    40     if modexact is being used exclusively then that's not reached.  */
    41  
    42  int
    43  mpz_congruent_ui_p (mpz_srcptr a, unsigned long cu, unsigned long du)
    44  {
    45    mp_srcptr  ap;
    46    mp_size_t  asize;
    47    mp_limb_t  c, d, r;
    48  
    49    if (UNLIKELY (du == 0))
    50      return (mpz_cmp_ui (a, cu) == 0);
    51  
    52    asize = SIZ(a);
    53    if (asize == 0)
    54      {
    55        if (cu < du)
    56  	return cu == 0;
    57        else
    58  	return (cu % du) == 0;
    59      }
    60  
    61    /* For nails don't try to be clever if c or d is bigger than a limb, just
    62       fake up some mpz_t's and go to the main mpz_congruent_p.  */
    63    if (du > GMP_NUMB_MAX || cu > GMP_NUMB_MAX)
    64      {
    65        mp_limb_t  climbs[2], dlimbs[2];
    66        mpz_t      cz, dz;
    67  
    68        ALLOC(cz) = 2;
    69        PTR(cz) = climbs;
    70        ALLOC(dz) = 2;
    71        PTR(dz) = dlimbs;
    72  
    73        mpz_set_ui (cz, cu);
    74        mpz_set_ui (dz, du);
    75        return mpz_congruent_p (a, cz, dz);
    76      }
    77  
    78    /* NEG_MOD works on limbs, so convert ulong to limb */
    79    c = cu;
    80    d = du;
    81  
    82    if (asize < 0)
    83      {
    84        asize = -asize;
    85        NEG_MOD (c, c, d);
    86      }
    87  
    88    ap = PTR (a);
    89  
    90    if (ABOVE_THRESHOLD (asize, BMOD_1_TO_MOD_1_THRESHOLD))
    91      {
    92        r = mpn_mod_1 (ap, asize, d);
    93        if (c < d)
    94  	return r == c;
    95        else
    96  	return r == (c % d);
    97      }
    98  
    99    if ((d & 1) == 0)
   100      {
   101        /* Strip low zero bits to get odd d required by modexact.  If
   102  	 d==e*2^n then a==c mod d if and only if both a==c mod 2^n
   103  	 and a==c mod e.  */
   104  
   105        unsigned	twos;
   106  
   107        if ((ap[0]-c) & LOW_ZEROS_MASK (d))
   108  	return 0;
   109  
   110        count_trailing_zeros (twos, d);
   111        d >>= twos;
   112      }
   113  
   114    r = mpn_modexact_1c_odd (ap, asize, d, c);
   115    return r == 0 || r == d;
   116  }