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/* mpz_remove -- divide out a factor and return its multiplicity.
Copyright 1998-2002, 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 https://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 x, rem;
mpz_init (rem);
mpz_init (x);
pwr = 0;
mpz_tdiv_qr (x, rem, src, f);
if (SIZ (rem) == 0)
{
mpz_t fpow[GMP_LIMB_BITS]; /* Really MP_SIZE_T_BITS */
int p;
#if WANT_ORIGINAL_DEST
mp_ptr dp;
dp = PTR (dest);
#endif
/* 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_set (fpow[0], f);
mpz_swap (dest, x);
p = 1;
/* Divide by f, f^2 ... f^(2^k) until we get a remainder for f^(2^k). */
while (ABSIZ (dest) >= 2 * ABSIZ (fpow[p - 1]) - 1)
{
mpz_init (fpow[p]);
mpz_mul (fpow[p], fpow[p - 1], fpow[p - 1]);
mpz_tdiv_qr (x, rem, dest, fpow[p]);
if (SIZ (rem) != 0) {
mpz_clear (fpow[p]);
break;
}
mpz_swap (dest, x);
p++;
}
pwr = ((mp_bitcnt_t)1 << p) - 1;
/* 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_swap (dest, x);
}
mpz_clear (fpow[p]);
}
#if WANT_ORIGINAL_DEST
if (PTR (x) == dp) {
mpz_swap (dest, x);
mpz_set (dest, x);
}
#endif
}
else
mpz_set (dest, src);
mpz_clear (x);
mpz_clear (rem);
}
return pwr;
}
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