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

1.1       ohara       1: /* mpz_divisible_ui_p -- mpz by ulong divisibility test.
                      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: int
                     28: mpz_divisible_ui_p (mpz_srcptr a, unsigned long d)
                     29: {
                     30:   mp_size_t  asize;
                     31:   mp_ptr     ap;
                     32:   unsigned   twos;
                     33:
                     34:   if (d == 0)
                     35:     DIVIDE_BY_ZERO;
                     36:
                     37:   asize = SIZ(a);
                     38:   if (asize == 0)  /* 0 divisible by any d */
                     39:     return 1;
                     40:
                     41:   /* For nails don't try to be clever if d is bigger than a limb, just fake
                     42:      up an mpz_t and go to the main mpz_divisible_p.  */
                     43:   if (d > GMP_NUMB_MAX)
                     44:     {
                     45:       mp_limb_t  dlimbs[2];
                     46:       mpz_t      dz;
                     47:       ALLOC(dz) = 2;
                     48:       PTR(dz) = dlimbs;
                     49:       mpz_set_ui (dz, d);
                     50:       return mpz_divisible_p (a, dz);
                     51:     }
                     52:
                     53:   ap = PTR(a);
                     54:   asize = ABS(asize);  /* ignore sign of a */
                     55:
                     56:   if (BELOW_THRESHOLD (asize, MODEXACT_1_ODD_THRESHOLD))
                     57:     return mpn_mod_1 (ap, asize, (mp_limb_t) d) == 0;
                     58:
                     59:   if (! (d & 1))
                     60:     {
                     61:       /* Strip low zero bits to get odd d required by modexact.  If d==e*2^n
                     62:          and a is divisible by 2^n and by e, then it's divisible by d. */
                     63:
                     64:       if ((ap[0] & LOW_ZEROS_MASK (d)) != 0)
                     65:         return 0;
                     66:
                     67:       count_trailing_zeros (twos, (mp_limb_t) d);
                     68:       d >>= twos;
                     69:     }
                     70:
                     71:   return mpn_modexact_1_odd (ap, asize, (mp_limb_t) d) == 0;
                     72: }