73 lines
2.0 KiB
C
73 lines
2.0 KiB
C
/* mpz_divisible_ui_p -- mpz by ulong divisibility test.
|
|
|
|
Copyright 2000, 2001, 2002 Free Software Foundation, Inc.
|
|
|
|
This file is part of the GNU MP Library.
|
|
|
|
The GNU MP Library is free software; you can redistribute it and/or modify
|
|
it under the terms of the GNU Lesser General Public License as published by
|
|
the Free Software Foundation; either version 2.1 of the License, or (at your
|
|
option) any later version.
|
|
|
|
The GNU MP Library is distributed in the hope that it will be useful, but
|
|
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
|
|
or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
|
|
License for more details.
|
|
|
|
You should have received a copy of the GNU Lesser General Public License
|
|
along with the GNU MP Library; see the file COPYING.LIB. If not, write to
|
|
the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
|
|
MA 02110-1301, USA. */
|
|
|
|
#include "gmp.h"
|
|
#include "gmp-impl.h"
|
|
#include "longlong.h"
|
|
|
|
|
|
int
|
|
mpz_divisible_ui_p (mpz_srcptr a, unsigned long d)
|
|
{
|
|
mp_size_t asize;
|
|
mp_ptr ap;
|
|
unsigned twos;
|
|
|
|
asize = SIZ(a);
|
|
if (UNLIKELY (d == 0))
|
|
return (asize == 0);
|
|
|
|
if (asize == 0) /* 0 divisible by any d */
|
|
return 1;
|
|
|
|
/* For nails don't try to be clever if d is bigger than a limb, just fake
|
|
up an mpz_t and go to the main mpz_divisible_p. */
|
|
if (d > GMP_NUMB_MAX)
|
|
{
|
|
mp_limb_t dlimbs[2];
|
|
mpz_t dz;
|
|
ALLOC(dz) = 2;
|
|
PTR(dz) = dlimbs;
|
|
mpz_set_ui (dz, d);
|
|
return mpz_divisible_p (a, dz);
|
|
}
|
|
|
|
ap = PTR(a);
|
|
asize = ABS(asize); /* ignore sign of a */
|
|
|
|
if (BELOW_THRESHOLD (asize, MODEXACT_1_ODD_THRESHOLD))
|
|
return mpn_mod_1 (ap, asize, (mp_limb_t) d) == 0;
|
|
|
|
if (! (d & 1))
|
|
{
|
|
/* Strip low zero bits to get odd d required by modexact. If d==e*2^n
|
|
and a is divisible by 2^n and by e, then it's divisible by d. */
|
|
|
|
if ((ap[0] & LOW_ZEROS_MASK (d)) != 0)
|
|
return 0;
|
|
|
|
count_trailing_zeros (twos, (mp_limb_t) d);
|
|
d >>= twos;
|
|
}
|
|
|
|
return mpn_modexact_1_odd (ap, asize, (mp_limb_t) d) == 0;
|
|
}
|