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Annotation of OpenXM_contrib/gmp/mpz/divis_ui.c, Revision 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: }