| /* mpz_divexact -- finds quotient when known that quot * den == num && den != 0. |
| |
| Copyright 1991, 1993, 1994, 1995, 1996, 1997, 1998, 2000, 2001, 2002, 2005, |
| 2006, 2007 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 http://www.gnu.org/licenses/. */ |
| |
| /* 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 |
| mpz_divexact (mpz_ptr quot, mpz_srcptr num, mpz_srcptr den) |
| { |
| mp_ptr qp, tp; |
| mp_size_t qsize, tsize; |
| mp_srcptr np, dp; |
| mp_size_t nsize, dsize; |
| TMP_DECL; |
| |
| #if WANT_ASSERT |
| { |
| mpz_t rem; |
| mpz_init (rem); |
| mpz_tdiv_r (rem, num, den); |
| ASSERT (SIZ(rem) == 0); |
| mpz_clear (rem); |
| } |
| #endif |
| |
| nsize = ABS (num->_mp_size); |
| dsize = ABS (den->_mp_size); |
| |
| qsize = nsize - dsize + 1; |
| if (quot->_mp_alloc < qsize) |
| _mpz_realloc (quot, qsize); |
| |
| np = num->_mp_d; |
| dp = den->_mp_d; |
| qp = quot->_mp_d; |
| |
| if (nsize < dsize) |
| { |
| /* This special case avoids segfaults below when the function is |
| incorrectly called with |N| < |D|, N != 0. It also handles the |
| well-defined case N = 0. */ |
| quot->_mp_size = 0; |
| return; |
| } |
| |
| if (dsize <= 1) |
| { |
| if (dsize == 1) |
| { |
| MPN_DIVREM_OR_DIVEXACT_1 (qp, np, nsize, dp[0]); |
| qsize -= qp[qsize - 1] == 0; |
| quot->_mp_size = (num->_mp_size ^ den->_mp_size) >= 0 ? qsize : -qsize; |
| return; |
| } |
| |
| /* Generate divide-by-zero error since dsize == 0. */ |
| DIVIDE_BY_ZERO; |
| } |
| |
| /* Avoid quadratic behaviour, but do it conservatively. */ |
| if (qsize > 1500) |
| { |
| mpz_tdiv_q (quot, num, den); |
| return; |
| } |
| |
| TMP_MARK; |
| |
| /* 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) != 0) |
| { |
| if (quot == den) /* QUOT and DEN overlap. */ |
| { |
| tp = (mp_ptr) TMP_ALLOC (tsize * BYTES_PER_MP_LIMB); |
| MPN_COPY (tp, dp, tsize); |
| } |
| else |
| tp = (mp_ptr) dp; |
| if (qp != np) |
| MPN_COPY_INCR (qp, np, qsize); |
| } |
| else |
| { |
| unsigned int r; |
| tp = (mp_ptr) TMP_ALLOC (tsize * BYTES_PER_MP_LIMB); |
| count_trailing_zeros (r, dp[0]); |
| mpn_rshift (tp, dp, tsize, r); |
| if (dsize > tsize) |
| tp[tsize - 1] |= (dp[tsize] << (GMP_NUMB_BITS - r)) & GMP_NUMB_MASK; |
| mpn_rshift (qp, np, qsize, r); |
| if (nsize > qsize) |
| qp[qsize - 1] |= (np[qsize] << (GMP_NUMB_BITS - r)) & GMP_NUMB_MASK; |
| } |
| |
| /* Now QUOT <-- QUOT/T. */ |
| mpn_bdivmod (qp, qp, qsize, tp, tsize, qsize * GMP_NUMB_BITS); |
| MPN_NORMALIZE (qp, qsize); |
| |
| quot->_mp_size = (num->_mp_size ^ den->_mp_size) >= 0 ? qsize : -qsize; |
| |
| TMP_FREE; |
| } |