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Annotation of OpenXM_contrib/gmp/mpz/cong_ui.c, Revision 1.1.1.1

1.1       ohara       1: /* mpz_congruent_ui_p -- test congruence of mpz and ulong.
                      2:
                      3: Copyright 2000, 2001, 2002 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 the GNU Lesser General Public License as published by
                      9: the Free Software Foundation; either version 2.1 of the License, or (at your
                     10: option) any later version.
                     11:
                     12: The GNU MP Library is distributed in the hope that it will be useful, but
                     13: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
                     14: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
                     15: License for more details.
                     16:
                     17: You should have received a copy of the GNU Lesser General Public License
                     18: along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
                     19: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
                     20: MA 02111-1307, USA. */
                     21:
                     22: #include "gmp.h"
                     23: #include "gmp-impl.h"
                     24: #include "longlong.h"
                     25:
                     26:
                     27: /* There's some explicit checks for c<d since it seems reasonably likely an
                     28:    application might use that in a test.
                     29:
                     30:    Hopefully the compiler can generate something good for r==(c%d), though
                     31:    if modexact is being used exclusively then that's not reached.  */
                     32:
                     33: int
                     34: mpz_congruent_ui_p (mpz_srcptr a, unsigned long cu, unsigned long du)
                     35: {
                     36:   mp_srcptr  ap;
                     37:   mp_size_t  asize;
                     38:   mp_limb_t  c, d, r;
                     39:
                     40:   if (du == 0)
                     41:     DIVIDE_BY_ZERO;
                     42:
                     43:   asize = SIZ(a);
                     44:   if (asize == 0)
                     45:     {
                     46:       if (cu < du)
                     47:         return cu == 0;
                     48:       else
                     49:         return (cu % du) == 0;
                     50:     }
                     51:
                     52:   /* For nails don't try to be clever if c or d is bigger than a limb, just
                     53:      fake up some mpz_t's and go to the main mpz_congruent_p.  */
                     54:   if (du > GMP_NUMB_MAX || cu > GMP_NUMB_MAX)
                     55:     {
                     56:       mp_limb_t  climbs[2], dlimbs[2];
                     57:       mpz_t      cz, dz;
                     58:
                     59:       ALLOC(cz) = 2;
                     60:       PTR(cz) = climbs;
                     61:       ALLOC(dz) = 2;
                     62:       PTR(dz) = dlimbs;
                     63:
                     64:       mpz_set_ui (cz, cu);
                     65:       mpz_set_ui (dz, du);
                     66:       return mpz_congruent_p (a, cz, dz);
                     67:     }
                     68:
                     69:   /* NEG_MOD works on limbs, so convert ulong to limb */
                     70:   c = cu;
                     71:   d = du;
                     72:
                     73:   if (asize < 0)
                     74:     {
                     75:       asize = -asize;
                     76:       NEG_MOD (c, c, d);
                     77:     }
                     78:
                     79:   ap = PTR (a);
                     80:
                     81:   if (BELOW_THRESHOLD (asize, MODEXACT_1_ODD_THRESHOLD))
                     82:     {
                     83:       r = mpn_mod_1 (ap, asize, d);
                     84:       if (c < d)
                     85:         return r == c;
                     86:       else
                     87:         return r == (c % d);
                     88:     }
                     89:
                     90:   if ((d & 1) == 0)
                     91:     {
                     92:       /* Strip low zero bits to get odd d required by modexact.  If
                     93:          d==e*2^n then a==c mod d if and only if both a==c mod 2^n
                     94:          and a==c mod e.  */
                     95:
                     96:       unsigned  twos;
                     97:
                     98:       if ((ap[0]-c) & LOW_ZEROS_MASK (d))
                     99:         return 0;
                    100:
                    101:       count_trailing_zeros (twos, d);
                    102:       d >>= twos;
                    103:     }
                    104:
                    105:   r = mpn_modexact_1c_odd (ap, asize, d, c);
                    106:   return r == 0 || r == d;
                    107: }