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/* mpz_remove -- divide out a factor and return its multiplicity.
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Copyright 1998-2002, 2012 Free Software Foundation, Inc.
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This file is part of the GNU MP Library.
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The GNU MP Library is free software; you can redistribute it and/or modify
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it under the terms of either:
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* the GNU Lesser General Public License as published by the Free
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Software Foundation; either version 3 of the License, or (at your
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option) any later version.
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or
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* the GNU General Public License as published by the Free Software
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Foundation; either version 2 of the License, or (at your option) any
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later version.
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or both in parallel, as here.
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The GNU MP Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received copies of the GNU General Public License and the
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GNU Lesser General Public License along with the GNU MP Library. If not,
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see https://www.gnu.org/licenses/. */
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#include "gmp.h"
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#include "gmp-impl.h"
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mp_bitcnt_t
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mpz_remove (mpz_ptr dest, mpz_srcptr src, mpz_srcptr f)
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{
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mp_bitcnt_t pwr;
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mp_srcptr fp;
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mp_size_t sn, fn, afn;
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mp_limb_t fp0;
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sn = SIZ (src);
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fn = SIZ (f);
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fp = PTR (f);
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afn = ABS (fn);
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fp0 = fp[0];
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if (UNLIKELY ((afn <= (fp0 == 1)) /* mpz_cmpabs_ui (f, 1) <= 0 */
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| (sn == 0)))
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{
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/* f = 0 or f = +- 1 or src = 0 */
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if (afn == 0)
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DIVIDE_BY_ZERO;
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mpz_set (dest, src);
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return 0;
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}
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if ((fp0 & 1) != 0)
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{ /* f is odd */
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mp_ptr dp;
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mp_size_t dn;
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dn = ABS (sn);
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dp = MPZ_REALLOC (dest, dn);
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pwr = mpn_remove (dp, &dn, PTR(src), dn, PTR(f), afn, ~(mp_bitcnt_t) 0);
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SIZ (dest) = ((pwr & (fn < 0)) ^ (sn < 0)) ? -dn : dn;
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}
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else if (afn == (fp0 == 2))
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{ /* mpz_cmpabs_ui (f, 2) == 0 */
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pwr = mpz_scan1 (src, 0);
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mpz_div_2exp (dest, src, pwr);
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if (pwr & (fn < 0)) /*((pwr % 2 == 1) && (SIZ (f) < 0))*/
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mpz_neg (dest, dest);
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}
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else
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{ /* f != +-2 */
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mpz_t x, rem;
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mpz_init (rem);
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mpz_init (x);
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pwr = 0;
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mpz_tdiv_qr (x, rem, src, f);
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if (SIZ (rem) == 0)
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{
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mpz_t fpow[GMP_LIMB_BITS]; /* Really MP_SIZE_T_BITS */
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int p;
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#if WANT_ORIGINAL_DEST
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mp_ptr dp;
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dp = PTR (dest);
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#endif
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/* We could perhaps compute mpz_scan1(src,0)/mpz_scan1(f,0). It is an
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upper bound of the result we're seeking. We could also shift down the
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operands so that they become odd, to make intermediate values
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smaller. */
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mpz_init_set (fpow[0], f);
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mpz_swap (dest, x);
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p = 1;
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/* Divide by f, f^2 ... f^(2^k) until we get a remainder for f^(2^k). */
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while (ABSIZ (dest) >= 2 * ABSIZ (fpow[p - 1]) - 1)
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{
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mpz_init (fpow[p]);
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mpz_mul (fpow[p], fpow[p - 1], fpow[p - 1]);
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mpz_tdiv_qr (x, rem, dest, fpow[p]);
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if (SIZ (rem) != 0) {
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mpz_clear (fpow[p]);
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break;
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}
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mpz_swap (dest, x);
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p++;
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}
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pwr = ((mp_bitcnt_t)1 << p) - 1;
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/* Divide by f^(2^(k-1)), f^(2^(k-2)), ..., f for all divisors that give
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a zero remainder. */
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while (--p >= 0)
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{
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mpz_tdiv_qr (x, rem, dest, fpow[p]);
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if (SIZ (rem) == 0)
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{
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pwr += (mp_bitcnt_t)1 << p;
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mpz_swap (dest, x);
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}
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mpz_clear (fpow[p]);
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}
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#if WANT_ORIGINAL_DEST
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if (PTR (x) == dp) {
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mpz_swap (dest, x);
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mpz_set (dest, x);
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}
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#endif
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}
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else
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mpz_set (dest, src);
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mpz_clear (x);
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mpz_clear (rem);
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}
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return pwr;
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}
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