136 lines
3.8 KiB
C
136 lines
3.8 KiB
C
/* mpz_divexact -- finds quotient when known that quot * den == num && den != 0.
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Copyright 1991, 1993, 1994, 1995, 1996, 1997, 1998, 2000, 2001, 2002, 2005, 2006
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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 the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or (at your
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option) any later version.
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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 Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with the GNU MP Library; see the file COPYING.LIB. If not, write to
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the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
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MA 02110-1301, USA. */
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/* Ken Weber (kweber@mat.ufrgs.br, kweber@mcs.kent.edu)
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Funding for this work has been partially provided by Conselho Nacional
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de Desenvolvimento Cienti'fico e Tecnolo'gico (CNPq) do Brazil, Grant
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301314194-2, and was done while I was a visiting reseacher in the Instituto
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de Matema'tica at Universidade Federal do Rio Grande do Sul (UFRGS).
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References:
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T. Jebelean, An algorithm for exact division, Journal of Symbolic
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Computation, v. 15, 1993, pp. 169-180. */
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#include "gmp.h"
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#include "gmp-impl.h"
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#include "longlong.h"
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void
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mpz_divexact (mpz_ptr quot, mpz_srcptr num, mpz_srcptr den)
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{
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mp_ptr qp, tp;
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mp_size_t qsize, tsize;
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mp_srcptr np, dp;
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mp_size_t nsize, dsize;
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TMP_DECL;
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#if WANT_ASSERT
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{
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mpz_t rem;
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mpz_init (rem);
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mpz_tdiv_r (rem, num, den);
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ASSERT (SIZ(rem) == 0);
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mpz_clear (rem);
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}
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#endif
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nsize = ABS (num->_mp_size);
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dsize = ABS (den->_mp_size);
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qsize = nsize - dsize + 1;
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if (quot->_mp_alloc < qsize)
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_mpz_realloc (quot, qsize);
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np = num->_mp_d;
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dp = den->_mp_d;
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qp = quot->_mp_d;
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if (nsize == 0)
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{
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if (dsize == 0)
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DIVIDE_BY_ZERO;
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quot->_mp_size = 0;
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return;
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}
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if (dsize <= 1)
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{
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if (dsize == 1)
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{
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MPN_DIVREM_OR_DIVEXACT_1 (qp, np, nsize, dp[0]);
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qsize -= qp[qsize - 1] == 0;
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quot->_mp_size = (num->_mp_size ^ den->_mp_size) >= 0 ? qsize : -qsize;
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return;
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}
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/* Generate divide-by-zero error since dsize == 0. */
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DIVIDE_BY_ZERO;
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}
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/* Avoid quadratic behaviour, but do it conservatively. */
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if (qsize > 1500)
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{
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mpz_tdiv_q (quot, num, den);
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return;
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}
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TMP_MARK;
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/* QUOT <-- NUM/2^r, T <-- DEN/2^r where = r number of twos in DEN. */
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while (dp[0] == 0)
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np += 1, nsize -= 1, dp += 1, dsize -= 1;
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tsize = MIN (qsize, dsize);
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if ((dp[0] & 1) != 0)
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{
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if (quot == den) /* QUOT and DEN overlap. */
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{
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tp = (mp_ptr) TMP_ALLOC (tsize * BYTES_PER_MP_LIMB);
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MPN_COPY (tp, dp, tsize);
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}
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else
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tp = (mp_ptr) dp;
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if (qp != np)
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MPN_COPY_INCR (qp, np, qsize);
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}
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else
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{
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unsigned int r;
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tp = (mp_ptr) TMP_ALLOC (tsize * BYTES_PER_MP_LIMB);
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count_trailing_zeros (r, dp[0]);
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mpn_rshift (tp, dp, tsize, r);
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if (dsize > tsize)
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tp[tsize - 1] |= (dp[tsize] << (GMP_NUMB_BITS - r)) & GMP_NUMB_MASK;
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mpn_rshift (qp, np, qsize, r);
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if (nsize > qsize)
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qp[qsize - 1] |= (np[qsize] << (GMP_NUMB_BITS - r)) & GMP_NUMB_MASK;
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}
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/* Now QUOT <-- QUOT/T. */
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mpn_bdivmod (qp, qp, qsize, tp, tsize, qsize * GMP_NUMB_BITS);
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MPN_NORMALIZE (qp, qsize);
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quot->_mp_size = (num->_mp_size ^ den->_mp_size) >= 0 ? qsize : -qsize;
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TMP_FREE;
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}
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