/*============================================================================= This file is part of FLINT. FLINT is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. FLINT 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 General Public License for more details. You should have received a copy of the GNU General Public License along with FLINT; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA =============================================================================*/ /****************************************************************************** Copyright (C) 2011 William Hart ******************************************************************************/ #include #include "flint.h" #include "fmpz.h" #include "fmpz_vec.h" #include "fmpz_poly.h" #include "mpn_extras.h" /* Divide (arrayg, limbsg) by the positive value gc inplace and return the number of limbs written */ mp_size_t flint_mpn_tdiv_q_fmpz_inplace(mp_ptr arrayg, mp_size_t limbsg, fmpz_t gc) { if (fmpz_size(gc) == 1) { mpn_divmod_1(arrayg, arrayg, limbsg, fmpz_get_ui(gc)); return limbsg - (arrayg[limbsg - 1] == 0); } else { mp_size_t tlimbs; __mpz_struct * mpz_ptr = COEFF_TO_PTR(*gc); mp_ptr temp = flint_malloc(limbsg*sizeof(mp_limb_t)); flint_mpn_copyi(temp, arrayg, limbsg); mpn_tdiv_q(arrayg, temp, limbsg, mpz_ptr->_mp_d, mpz_ptr->_mp_size); tlimbs = limbsg - mpz_ptr->_mp_size + 1; tlimbs -= (arrayg[tlimbs - 1] == 0); flint_free(temp); return tlimbs; } } /* Returns 1 if sign * (G, glen) * (Q, qlen) = (P, len), else returns 0. Temp requires space for glen + qlen - 1 coefficients */ int multiplies_out(fmpz * P, slong len, const fmpz * Q, slong qlen, const fmpz * G, slong glen, slong sign, fmpz * temp) { int divides = 0; /* multiply out */ if (qlen >= glen) _fmpz_poly_mul(temp, Q, qlen, G, glen); else _fmpz_poly_mul(temp, G, glen, Q, qlen); if (sign < WORD(0)) _fmpz_vec_neg(temp, temp, glen + qlen - 1); /* check if quotient really was exact */ divides = (glen + qlen - 1 == len && _fmpz_vec_equal(temp, P, len)); return divides; } /* Assumes len1 != 0 != len2 */ int _fmpz_poly_gcd_heuristic(fmpz * res, const fmpz * poly1, slong len1, const fmpz * poly2, slong len2) { ulong bits1, bits2, max_bits, pack_bits, bound_bits, bits_G, bits_Q; ulong limbs1, limbs2, limbsg, pack_limbs, qlimbs; ulong log_glen, log_length; slong sign1, sign2, glen, qlen; fmpz_t ac, bc, d, gc; fmpz * A, * B, * G, * Q, * t; mp_ptr array1, array2, arrayg, q, temp; int divides; fmpz_init(ac); fmpz_init(bc); fmpz_init(d); /* compute gcd of content of poly1 and poly2 */ _fmpz_poly_content(ac, poly1, len1); _fmpz_poly_content(bc, poly2, len2); fmpz_gcd(d, ac, bc); /* special case, one of the polys is a constant */ if (len2 == 1) /* if len1 == 1 then so does len2 */ { fmpz_set(res, d); fmpz_clear(ac); fmpz_clear(bc); fmpz_clear(d); return 1; } /* divide poly1 and poly2 by their content */ A = _fmpz_vec_init(len1); B = _fmpz_vec_init(len2); _fmpz_vec_scalar_divexact_fmpz(A, poly1, len1, ac); _fmpz_vec_scalar_divexact_fmpz(B, poly2, len2, bc); fmpz_clear(ac); fmpz_clear(bc); /* special case, one of the polys is length 2 */ if (len2 == 2) /* if len1 == 2 then so does len2 */ { Q = _fmpz_vec_init(len1 - len2 + 1); if (_fmpz_poly_divides(Q, A, len1, B, 2)) { _fmpz_vec_scalar_mul_fmpz(res, B, 2, d); if (fmpz_sgn(res + 1) < 0) _fmpz_vec_neg(res, res, 2); } else { fmpz_set(res, d); fmpz_zero(res + 1); } fmpz_clear(d); _fmpz_vec_clear(A, len1); _fmpz_vec_clear(B, len2); _fmpz_vec_clear(Q, len1 - len2 + 1); return 1; } /* Determine how many bits (pack_bits) to pack into. The bound bound_bits ensures that if G | A and G | B with G primitive then G is the gcd of A and B. The bound is taken from http://arxiv.org/abs/cs/0206032v1 */ bits1 = FLINT_ABS(_fmpz_vec_max_bits(A, len1)); bits2 = FLINT_ABS(_fmpz_vec_max_bits(B, len2)); max_bits = FLINT_MAX(bits1, bits2); bound_bits = FLINT_MIN(bits1, bits2) + 6; pack_bits = FLINT_MAX(bound_bits, max_bits); /* need to pack original polys */ pack_limbs = (pack_bits - 1)/FLINT_BITS + 1; if (pack_bits >= 32) /* pack into multiples of limbs if >= 32 bits */ pack_bits = FLINT_BITS*pack_limbs; /* allocate space to pack into */ limbs1 = (pack_bits*len1 - 1)/FLINT_BITS + 1; limbs2 = (pack_bits*len2 - 1)/FLINT_BITS + 1; array1 = flint_calloc(limbs1, sizeof(mp_limb_t)); array2 = flint_calloc(limbs2, sizeof(mp_limb_t)); arrayg = flint_calloc(limbs2, sizeof(mp_limb_t)); /* pack first poly and normalise */ sign1 = (slong) fmpz_sgn(A + len1 - 1); _fmpz_poly_bit_pack(array1, A, len1, pack_bits, sign1); while (array1[limbs1 - 1] == 0) limbs1--; /* pack second poly and normalise */ sign2 = (slong) fmpz_sgn(B + len2 - 1); _fmpz_poly_bit_pack(array2, B, len2, pack_bits, sign2); while (array2[limbs2 - 1] == 0) limbs2--; /* compute integer GCD */ limbsg = flint_mpn_gcd_full(arrayg, array1, limbs1, array2, limbs2); /* Make space for unpacked gcd. May have one extra coeff due to 1 0 -x being packed as 0 -1 -x. */ glen = FLINT_MIN((limbsg*FLINT_BITS)/pack_bits + 1, len2); G = _fmpz_vec_init(glen); /* clear bits after g in arrayg so they are not inadvertently pulled into G after bit unpacking */ flint_mpn_zero(arrayg + limbsg, limbs2-limbsg); /* unpack gcd */ _fmpz_poly_bit_unpack(G, glen, arrayg, pack_bits, 0); while (G[glen - 1] == 0) glen--; /* divide by any content */ fmpz_init(gc); _fmpz_poly_content(gc, G, glen); if (!fmpz_is_one(gc)) limbsg = flint_mpn_tdiv_q_fmpz_inplace(arrayg, limbsg, gc); /* make space for quotient and remainder of first poly by gcd */ qlimbs = limbs1 - limbsg + 1; qlen = FLINT_MIN(len1, (qlimbs*FLINT_BITS)/pack_bits + 1); qlimbs = (qlen*pack_bits - 1)/FLINT_BITS + 1; q = flint_calloc(qlimbs, sizeof(mp_limb_t)); temp = flint_malloc(limbsg*sizeof(mp_limb_t)); divides = 0; if (flint_mpn_divides(q, array1, limbs1, arrayg, limbsg, temp)) { /* unpack quotient of first poly by gcd */ Q = _fmpz_vec_init(len1); t = _fmpz_vec_init(len1 + glen); _fmpz_poly_bit_unpack(Q, qlen, q, pack_bits, 0); while (Q[qlen - 1] == 0) qlen--; /* divide by content */ _fmpz_vec_scalar_divexact_fmpz(G, G, glen, gc); /* check if we really need to multiply out to check for exact quotient */ bits_G = FLINT_ABS(_fmpz_vec_max_bits(G, glen)); bits_Q = FLINT_ABS(_fmpz_vec_max_bits(Q, qlen)); log_glen = FLINT_BIT_COUNT(glen); log_length = FLINT_MIN(log_glen, FLINT_BIT_COUNT(qlen)); divides = (bits_G + bits_Q + log_length < pack_bits); if (!divides) /* need to multiply out to check exact quotient */ divides = multiplies_out(A, len1, Q, qlen, G, glen, sign1, t); if (divides) /* quotient really was exact */ { flint_mpn_zero(q, qlimbs); if (flint_mpn_divides(q, array2, limbs2, arrayg, limbsg, temp)) { /* unpack quotient of second poly by gcd */ qlimbs = limbs2 - limbsg + 1; qlen = FLINT_MIN(len2, (qlimbs*FLINT_BITS - 1)/pack_bits + 1); _fmpz_poly_bit_unpack(Q, qlen, q, pack_bits, 0); while (Q[qlen - 1] == 0) qlen--; /* check if we really need to multiply out to check for exact quotient */ bits_Q = FLINT_ABS(_fmpz_vec_max_bits(Q, qlen)); log_length = FLINT_MIN(log_glen, FLINT_BIT_COUNT(qlen)); divides = (bits_G + bits_Q + log_length < pack_bits); if (!divides) /* we need to multiply out */ divides = multiplies_out(B, len2, Q, qlen, G, glen, sign1, t); } } _fmpz_vec_clear(t, len1 + glen); _fmpz_vec_clear(Q, len1); } flint_free(q); flint_free(temp); flint_free(arrayg); flint_free(array1); flint_free(array2); fmpz_clear(gc); _fmpz_vec_clear(A, len1); _fmpz_vec_clear(B, len2); /* we found the gcd, so multiply by content */ if (divides) { _fmpz_vec_zero(res + glen, len2 - glen); _fmpz_vec_scalar_mul_fmpz(res, G, glen, d); } fmpz_clear(d); _fmpz_vec_clear(G, glen); return divides; } int fmpz_poly_gcd_heuristic(fmpz_poly_t res, const fmpz_poly_t poly1, const fmpz_poly_t poly2) { if (poly1->length < poly2->length) { return fmpz_poly_gcd_heuristic(res, poly2, poly1); } else /* len1 >= len2 >= 0 */ { const slong len1 = poly1->length; const slong len2 = poly2->length; int done = 1; /* len1 = 0 or len2 = 0 need done = 1 */ if (len1 == 0) /* len1 = len2 = 0 */ { fmpz_poly_zero(res); } else if (len2 == 0) /* len1 > len2 = 0 */ { if (fmpz_sgn(poly1->coeffs + (len1 - 1)) > 0) fmpz_poly_set(res, poly1); else fmpz_poly_neg(res, poly1); } else /* len1 >= len2 >= 1 */ { /* underscore function automatically takes care of aliasing */ fmpz_poly_fit_length(res, len2); done = _fmpz_poly_gcd_heuristic(res->coeffs, poly1->coeffs, len1, poly2->coeffs, len2); if (done) { _fmpz_poly_set_length(res, len2); _fmpz_poly_normalise(res); } } return done; } }