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Annotation of OpenXM_contrib/gmp/mpz/divis_2exp.c, Revision 1.1

1.1     ! ohara       1: /* mpz_divisible_2exp_p -- mpz by 2^n divisibility test
        !             2:
        !             3: Copyright 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:
        !            25:
        !            26: int
        !            27: mpz_divisible_2exp_p (mpz_srcptr a, unsigned long d)
        !            28: {
        !            29:   unsigned long  i, dlimbs, dbits;
        !            30:   mp_ptr         ap;
        !            31:   mp_limb_t      dmask;
        !            32:   mp_size_t      asize;
        !            33:
        !            34:   asize = ABSIZ(a);
        !            35:   dlimbs = d / GMP_NUMB_BITS;
        !            36:
        !            37:   /* if d covers the whole of a, then only a==0 is divisible */
        !            38:   if (asize <= dlimbs)
        !            39:     return asize == 0;
        !            40:
        !            41:   /* whole limbs must be zero */
        !            42:   ap = PTR(a);
        !            43:   for (i = 0; i < dlimbs; i++)
        !            44:     if (ap[i] != 0)
        !            45:       return 0;
        !            46:
        !            47:   /* left over bits must be zero */
        !            48:   dbits = d % GMP_NUMB_BITS;
        !            49:   dmask = (CNST_LIMB(1) << dbits) - 1;
        !            50:   return (ap[dlimbs] & dmask) == 0;
        !            51: }