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/* mpz_remove -- divide out a factor and return its multiplicity.
Copyright (C) 1998 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 Library General Public License as published by
the Free Software Foundation; either version 2 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 Library General Public
License for more details.
You should have received a copy of the GNU Library General Public License
along with the GNU MP Library; see the file COPYING.LIB. If not, write to
the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
MA 02111-1307, USA. */
#include "gmp.h"
#include "gmp-impl.h"
unsigned long int
mpz_remove (mpz_ptr dest, mpz_srcptr src, mpz_srcptr f)
{
mpz_t fpow[40]; /* inexhastible...until year 2020 or so */
mpz_t x, rem;
unsigned long int pwr;
int p;
if (mpz_cmp_ui (f, 1) <= 0)
DIVIDE_BY_ZERO;
if (mpz_cmp_ui (f, 2) == 0)
{
unsigned long int s0;
s0 = mpz_scan1 (src, 0);
mpz_div_2exp (dest, src, s0);
return s0;
}
/* 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 (fpow[0]);
mpz_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 = (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 += 1 << p;
mpz_set (dest, x);
}
mpz_clear (fpow[p]);
}
mpz_clear (x);
mpz_clear (rem);
return pwr;
}
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