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/* mpz_remove -- divide out a factor and return its multiplicity.
Copyright 1998, 1999, 2000, 2001, 2002, 2012 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 3 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. If not, see http://www.gnu.org/licenses/. */
#include "gmp.h"
#include "gmp-impl.h"
mp_bitcnt_t
mpz_remove (mpz_ptr dest, mpz_srcptr src, mpz_srcptr f)
{
mp_bitcnt_t pwr;
mp_srcptr fp;
mp_size_t sn, fn, afn;
mp_limb_t fp0;
sn = SIZ (src);
fn = SIZ (f);
fp = PTR (f);
afn = ABS (fn);
fp0 = fp[0];
if (UNLIKELY ((afn <= (fp0 == 1)) /* mpz_cmpabs_ui (f, 1) <= 0 */
| (sn == 0)))
{
/* f = 0 or f = +- 1 or src = 0 */
if (afn == 0)
DIVIDE_BY_ZERO;
mpz_set (dest, src);
return 0;
}
if ((fp0 & 1) != 0)
{ /* f is odd */
mp_ptr dp;
mp_size_t dn;
dn = ABS (sn);
dp = MPZ_REALLOC (dest, dn);
pwr = mpn_remove (dp, &dn, PTR(src), dn, PTR(f), afn, ~(mp_bitcnt_t) 0);
SIZ (dest) = ((pwr & (fn < 0)) ^ (sn < 0)) ? -dn : dn;
}
else if (afn == (fp0 == 2))
{ /* mpz_cmpabs_ui (f, 2) == 0 */
pwr = mpz_scan1 (src, 0);
mpz_div_2exp (dest, src, pwr);
if (pwr & (fn < 0)) /*((pwr % 2 == 1) && (SIZ (f) < 0))*/
mpz_neg (dest, dest);
}
else
{ /* f != +-2 */
mpz_t fpow[GMP_LIMB_BITS]; /* Really MP_SIZE_T_BITS */
mpz_t x, rem;
int p;
/* We could perhaps compute mpz_scan1(src,0)/mpz_scan1(f,0). It is an
upper bound of the result we're seeking. We could also shift down the
operands so that they become odd, to make intermediate values
smaller. */
mpz_init (rem);
mpz_init (x);
pwr = 0;
mpz_init_set (fpow[0], f);
mpz_set (dest, src);
/* Divide by f, f^2 ... f^(2^k) until we get a remainder for f^(2^k). */
for (p = 0;; p++)
{
mpz_tdiv_qr (x, rem, dest, fpow[p]);
if (SIZ (rem) != 0)
break;
mpz_init (fpow[p + 1]);
mpz_mul (fpow[p + 1], fpow[p], fpow[p]);
mpz_set (dest, x);
}
pwr = ((mp_bitcnt_t)1 << p) - 1;
mpz_clear (fpow[p]);
/* Divide by f^(2^(k-1)), f^(2^(k-2)), ..., f for all divisors that give
a zero remainder. */
while (--p >= 0)
{
mpz_tdiv_qr (x, rem, dest, fpow[p]);
if (SIZ (rem) == 0)
{
pwr += (mp_bitcnt_t)1 << p;
mpz_set (dest, x);
}
mpz_clear (fpow[p]);
}
mpz_clear (x);
mpz_clear (rem);
}
return pwr;
}
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