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/* mpz_divexact -- finds quotient when known that quot * den == num && den != 0.
Copyright (C) 1991, 1993, 1994, 1995 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. */
/* Ken Weber (kweber@mat.ufrgs.br, kweber@mcs.kent.edu)
Funding for this work has been partially provided by Conselho Nacional
de Desenvolvimento Cienti'fico e Tecnolo'gico (CNPq) do Brazil, Grant
301314194-2, and was done while I was a visiting reseacher in the Instituto
de Matema'tica at Universidade Federal do Rio Grande do Sul (UFRGS).
References:
T. Jebelean, An algorithm for exact division, Journal of Symbolic
Computation, v. 15, 1993, pp. 169-180. */
#include "gmp.h"
#include "gmp-impl.h"
#include "longlong.h"
void
#if __STDC__
mpz_divexact (mpz_ptr quot, mpz_srcptr num, mpz_srcptr den)
#else
mpz_divexact (quot, num, den)
mpz_ptr quot;
mpz_srcptr num;
mpz_srcptr den;
#endif
{
mp_ptr qp, tp;
mp_size_t qsize, tsize;
mp_srcptr np = num->_mp_d;
mp_srcptr dp = den->_mp_d;
mp_size_t nsize = ABS (num->_mp_size);
mp_size_t dsize = ABS (den->_mp_size);
TMP_DECL (marker);
/* Generate divide-by-zero error if dsize == 0. */
if (dsize == 0)
{
quot->_mp_size = 1 / dsize;
return;
}
if (nsize == 0)
{
quot->_mp_size = 0;
return;
}
qsize = nsize - dsize + 1;
if (quot->_mp_alloc < qsize)
_mpz_realloc (quot, qsize);
qp = quot->_mp_d;
TMP_MARK (marker);
/* QUOT <-- NUM/2^r, T <-- DEN/2^r where = r number of twos in DEN. */
while (dp[0] == 0)
np += 1, nsize -= 1, dp += 1, dsize -= 1;
tsize = MIN (qsize, dsize);
if (dp[0] & 1)
{
if (qp != dp)
MPN_COPY (qp, np, qsize);
if (qp == dp) /* QUOT and DEN overlap. */
{
tp = (mp_ptr) TMP_ALLOC (sizeof (mp_limb_t) * tsize);
MPN_COPY (tp, dp, tsize);
}
else
tp = (mp_ptr) dp;
}
else
{
unsigned long int r;
tp = (mp_ptr) TMP_ALLOC (sizeof (mp_limb_t) * tsize);
count_trailing_zeros (r, dp[0]);
mpn_rshift (tp, dp, tsize, r);
if (dsize > tsize)
tp[tsize-1] |= dp[tsize] << (BITS_PER_MP_LIMB - r);
mpn_rshift (qp, np, qsize, r);
if (nsize > qsize)
qp[qsize-1] |= np[qsize] << (BITS_PER_MP_LIMB - r);
}
/* Now QUOT <-- QUOT/T. */
mpn_bdivmod (qp, qp, qsize, tp, tsize, qsize * BITS_PER_MP_LIMB);
MPN_NORMALIZE (qp, qsize);
quot->_mp_size = (num->_mp_size < 0) == (den->_mp_size < 0) ? qsize : -qsize;
TMP_FREE (marker);
}
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