Return to divis_2exp.c CVS log

Up to [local] / OpenXM_contrib / gmp / mpz

Annotation of OpenXM_contrib/gmp/mpz/divis_2exp.c, Revision 1.1.1.1

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: }