source/libs/gmp/gmp-src/mpz/cong_ui.c

   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 }